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Abstract: Sickle cell disease (SCD) is canonically characterized by reduced red blood cell (RBC) deformability, leading to microvascular obstruction and inflammation. Although the biophysical properties of sickle RBCs are known to influence SCD vasculopathy, the contribution of poor RBC deformability to endothelial dysfunction has yet to be fully explored. Leveraging interrelated in vitro and in silico approaches, we introduce a new paradigm of SCD vasculopathy in which poorly deformable sickle RBCs directly cause endothelial dysfunction via mechanotransduction, during which endothelial cells sense and pathophysiologically respond to aberrant physical forces independently of microvascular obstruction, adhesion, or hemolysis. We demonstrate that perfusion of sickle RBCs or pharmacologically-dehydrated healthy RBCs into small venule-sized "endothelialized" microfluidics leads to pathologic physical interactions with endothelial cells that directly induce inflammatory pathways. Using a combination of computational simulations and large venule-sized endothelialized microfluidics, we observed that perfusion of heterogeneous sickle RBC subpopulations with varying deformability, as well as suspensions of dehydrated normal RBCs admixed with normal RBCs, leads to aberrant margination of the less-deformable RBC subpopulations toward the vessel walls, causing localized, increased shear stress. Increased wall stress is dependent on the degree of subpopulation heterogeneity and oxygen tension and leads to inflammatory endothelial gene expression via mechanotransductive pathways. Our multifaceted approach demonstrates that the presence of sickle RBCs with reduced deformability leads directly to pathological physical (ie, direct collisions and/or compressive forces) and shear-mediated interactions with endothelial cells and induces an inflammatory response, thereby elucidating the ubiquity of vascular dysfunction in SCD., (© 2024 American Society of Hematology. Published by Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.)

In sickle cell anemia, deoxygenation causes erythrocytes to distort, while reoxygenation permits them to recover a normal biconcave disk shape. Irreversibly sickled cells (ISCs) remain distorted when reoxygenated and have been thought to have among the highest intracellular hemoglobin concentrations of the sickle red cell population and therefore the greatest vulnerability to vasoocclusion. Using a new optical method, which we describe, we have made precise measurements of the intracellular hemoglobin concentration, and intracellular O 2 saturation, of ISCs, as well as oxygenated sickle cells with a normal biconcave disc shape, and cells with shapes distorted by the sickle fibers they contain. This method also provides good estimates of cell volumes, and hemoglobin per red cell. The concentration distribution of the ISCs is found to be similar to normal, discoid cells. Average ISC volumes exceed their discoid counterparts, with a much broader distribution, arguing against dehydration as their origin. The concentration distribution of the polymer-laden sickled cells is significantly higher in mean value, and their volume distributions indicate some dehydration. Previous assumptions about ISCs may have thus been colored by the presence of sickle cells that did contain polymer, and true ISCs may be much more benign than once thought, which underscores the importance of accurate measurement on individual cells. This method could be used to follow changes in individual cell properties under various specific perturbations, and where characterization by flow cytometry is infeasible., Competing Interests: Declaration of interests All authors declare no conflicts of interest., (Copyright © 2024 Biophysical Society. Published by Elsevier Inc. All rights reserved.)

In recent times, automated detection of diseases from pathological images leveraging Machine Learning (ML) models has become fairly common, where the ML models learn detecting the disease by identifying biomarkers from the images. However, such an approach requires the models to be trained on a vast amount of data, and healthcare organizations often tend to limit access due to privacy concerns. Consequently, collecting data for traditional centralized training becomes challenging. These privacy concerns can be handled by Federation Learning (FL), which builds an unbiased global model from local models trained with client data while maintaining the confidentiality of local data. Using FL, this study solves the problem of centralized data collection by detecting deformations in images of Red Blood Cells (RBC) in a decentralized way. To achieve this, RBC data is used to train multiple Deep Learning (DL) models, and among the various DL models, the most efficient one is considered to be used as the global model inside the FL framework. The FL framework works by copying the global model's weight to the client's local models and then training the local models in client-specific devices to average the weights of the local model back to the global model. In the averaging process, direct averaging is performed and alongside, weighted averaging is also done to weigh the individual local model's contribution according to their performance, keeping the FL framework immune to the effects of bad clients and attacks. In the process, the data of the client remains confidential during training, while the global model learns necessary information. The results of the experiments indicate that there is no significant difference in the performance of the FL method and the best-performing DL model, as the best-performing DL model reaches an accuracy of 96% and the FL environment reaches 94%-95%. This study shows that the FL technique, in comparison to the classic DL methodology, can accomplish confidentiality secured RBC deformation classification from RBC images without substantially diminishing the accuracy of the categorization. Finally, the overall validity of the classification results has been verified by employing GradCam driven Explainable AI techniques., (© 2024. The Author(s).)

Abstract: Purpose : This study aimed to investigate the presence of schistocytes in patients with sepsis and its association with mortality and organ failure. Methods : We conducted a retrospective observational study at Shiga University of Medical Science Hospital, Japan, from January 2015 to April 2021. This study included patients diagnosed with sepsis or septic shock. Schistocytes were identified through daily hematological examinations. Moreover, data on mortality rates and organ failure based on Sequential Organ Failure Assessment scores were systematically collected and analyzed. Results : Schistocytes were detected in 41 of the 330 patients with sepsis. The presence of schistocytes was associated with significantly high 90-day and 1-year mortality rates (48.7% and 68.2%, respectively; P < 0.001). Patients with schistocytes exhibited higher Sequential Organ Failure Assessment scores, particularly in the coagulation and renal components, indicating more severe organ failure than that observed in patients without schistocytes. These findings persisted even after adjusting for confounding factors, such as age, sex, and baseline comorbidities. Additionally, we observed that patients with schistocytes required frequent red blood cells, further highlighting the severity of their conditions. Conclusion : Schistocytes are significantly associated with increased long-term mortality and organ failure in patients with sepsis. Their detection may provide crucial insights into disease severity, guide targeted therapeutic strategies, and potentially improve the long-term outcomes of sepsis management., Competing Interests: The authors report no conflicts of interest., (Copyright © 2024 by the Shock Society.)

Deformability and sickling of red blood cells (RBCs) from individuals with sickle cell trait (SCT) was evaluated under harsh biophysical conditions that mimic certain vascular beds in vivo. RBC deformability in osmotic-gradient ektacytometry was decreased in HbAS (SCT) compared to HbAA (wild-type) RBCs at supraphysiological osmolalities. RBC deformability was also measured by oxygen-gradient ektacytometry. Whereas RBC sickling was not observed under isotonic and neutral pH conditions, hypertonicity and acidosis alone or in combination induced reversible sickling of SCT RBC. These data suggest that hyperosmolality and/or acidosis enhance hypoxia-induced sickling of SCT RBC., (© 2024 British Society for Haematology and John Wiley & Sons Ltd.)

The presence of schistocytes can be responsible for spurious thrombocytosis and spuriously low red blood count (RBC). The hemoglobin concentration will be correct (as the method usually used, destroys the red cells and converts a substantial proportion of the hemoglobin to a stable pigment) but mean corpuscular hemoglobin (MCH) is falsely high. The platelets and RBC histograms of the full blood count analyzers play an important role in the identification of schistocytes and must be carefully analyzed before reporting the previously full blood count parameters. In patients in ECMO, where can be expected the presence of a small number of schistocytes, this evaluation is particularly important to avoid wrong clinical decisions., (Copyright © 2024 The Author(s). Published by Elsevier Masson SAS.. All rights reserved.)

In children with sickle cell disease (SCD), splenectomy is immediately beneficial for acute sequestration crises and hypersplenism (ASSC/HyS) but portends a long-term risk of asplenia-related complications. We retrieved peripheral and splenic red blood cells (RBCs) from 17 SCD children/teenagers undergoing partial splenectomy for ASSC/HyS, 12 adult subjects without RBC-related disease undergoing splenectomy (controls), five human spleens perfused ex vivo with Hb SS - and Hb AA -RBC, and quantified abnormal RBC by microscopy, spleen-mimetic RBC filtration, and adhesion assays. Spleens were analyzed by immunohistochemistry and transmission electron microscopy (TEM). In circulating blood of SCD and control subjects, dysmorphic (elongated/spherocytic) RBCs were <2%, while proportions of pocked-RBC were 4.3-fold higher in SCD children than in controls. Compared to controls, splenic RBCs were more frequently dysmorphic (29.3% vs. 0.4%), stiffer (42.2% vs. 12.4%), and adherent (206 vs. 22 adherent RBC/area) in SCD subjects. By TEM, both polymer-containing and homogenous RBC contributed to spleen congestion, resulting in 3.8-fold higher RBC population density in SCD spleens than in control spleens, predominantly in the cords. Perfused spleens with normal function displayed similar congestion and retention of dysmorphic RBC as SCD spleens. The population density of active macrophages was similar in SCD and control spleens, with a relative deficit in phagocytosis of polymer-containing RBC. Despite the existence of hyposplenism, splenectomy in SCD children removes an organ that still efficiently filters out potentially pathogenic altered RBC. Innovative treatments allowing fine-tuned reduction of RBC retention would alleviate spleen congestion, the major pathogenic process in ASSC/HyS, while preserving spleen protective functions for the future., (© 2024 The Author(s). American Journal of Hematology published by Wiley Periodicals LLC.)

A 6-year-old spayed female Scottish Fold cat presented with lethargy and anorexia. A complete blood cell count indicated severe anemia and mild thrombocytopenia. Examination of peripheral blood smears revealed marked changes in the erythroid lineage, including the presence of basophilic stippling and Howell-Jolly bodies as well as an increase in nucleated erythrocytes, polychromatophils, ovalocytes, and schistocytes. Additionally, some erythrocytes contained a ring or figure-eight shaped structure known as a Cabot ring, which were especially observed in polychromatophilic erythrocytes. Hemolytic diseases (Mycoplasma infection and IMHA) were diagnostically excluded, and the cat was treated through prednisolone administration, whole blood transfusion, and administration of vitamins (K2 and B12); however, the anemia progressively worsened. Cabot rings were observed until Day 22 and subsequently disappeared as the number of nucleated RBCs increased, and the erythrocyte lineage shifted to immature population. On Day 42, peripheral blood examination revealed further left shifting and appearance of many rubriblasts. The patient died at home on Day 43. Necropsy revealed neoplastic cells infiltrating the bone marrow and other organs, which were immunopositive to CD71 which is an erythroid lineage marker. In humans, Cabot rings have been observed in megaloblastic anemia, lead poisoning, myelodysplastic syndrome, and myelofibrosis; further, they are thought to be related to stressed bone marrow and dyserythropoiesis. This is the first case report of a cat with Cabot rings, which are suggestive of defects in erythroid lineage production., (© 2024 American Society for Veterinary Clinical Pathology.)

Schistocytes are fragmented red blood cells produced as a result of mechanical damage to erythrocytes, usually due to microangiopathic thrombotic diseases or mechanical factors. The early laboratory detection of schistocytes has a critical impact on the timely diagnosis, effective treatment, and positive prognosis of diseases such as thrombocytopenic purpura and hemolytic uremic syndrome. Due to the rapid development of science and technology, laboratory hematology has also advanced. The accuracy and efficiency of tests performed by fully automated hematology analyzers and fully automated morphology analyzers have been considerably improved. In recent years, substantial improvements in computing power and machine learning (ML) algorithm development have dramatically extended the limits of the potential of autonomous machines. The rapid development of machine learning and artificial intelligence (AI) has led to the iteration and upgrade of automated detection of schistocytes. However, along with significantly facilitated operation processes, AI has brought challenges. This review summarizes the progress in laboratory schistocyte detection, the relationship between schistocytes and clinical diseases, and the progress of AI in the detection of schistocytes. In addition, current challenges and possible solutions are discussed, as well as the great potential of AI techniques for schistocyte testing in peripheral blood., (© 2024 John Wiley & Sons Ltd.)

Background: The effectiveness of red cell transfusion in a given blood unit that relied on both quantity and quality of donated cells undoubtedly affects prognostic outcomes., Objective: We aimed to determine the frequency of subclinical functional hemoglobin and red cell abnormalities in donated blood of Fayoum University Hospital in Egypt. Additionally, to assess the usefulness of reticulocyte mean hemoglobin content (RET-He) and immature reticulocyte fraction (IRF) as screening measures for such abnormalities., Material and Methods: This cross-sectional study enrolled 200 volunteer blood donors who met the national standard criterion of blood donation. Complete blood count with reticulocyte parameters, serum ferritin, sickling test, G6PD assay, Mentzer index, and naked-eye single tube red cell osmotic fragility test were carried out., Results: Functional red cell abnormalities represented 44 % of this cohort. Out of them, 4.5 % had iron deficiency, 11 % had a positive sickling test, 19 % had G6PD deficiency, and 9.5 % had suspicious thalassemia. The sensitivity and specificity test for RET-He in selective identification of functional hemoglobin abnormalities in donated blood were 83.3 % and 61.2 %, respectively at a cutoff value of 26.9. Though there was no statistically significant effect of RET-He on the selective detection of G6PD deficiency, IRF had a statistically significant high level with a p-value of 0.04., Conclusion: Subclinical functional red cell abnormalities seem to be prevalent among blood donors. Reticulocyte/ erythrocyte indices could be useful screening tools for red cell abnormalities. Further studies are required for assessing the impact of transfusing such abnormalities to neonates and other critical recipients., Competing Interests: Conflict of Interest All authors declare there is no conflict of interest., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Sickle cell disease (SCD) is a genetic disorder that affects millions of individuals worldwide. Chronic anemia, hemolysis, and vasculopathy are associated with SCD, and their role has been well characterized. These symptoms stem from hemoglobin (Hb) polymerization, which is the primary event in the molecular pathogenesis of SCD and contributes to erythrocyte or red blood cell (RBC) sickling, stiffness, and vaso-occlusion. The disease is caused by a mutation at the sixth position of the β-globin gene, coding for sickle Hb (HbS) instead of normal adult Hb (HbA), which under hypoxic conditions polymerizes into rigid fibers to distort the shapes of the RBCs. Only a few therapies are available, with the universal effectiveness of recently approved therapies still being monitored. In this review, we first focus on how sickle RBCs have altered metabolism and then highlight how this understanding reveals potential targets involved in the pathogenesis of the disease, which can be leveraged to create novel therapeutics for SCD.

Red blood cell (RBC) morphology is, in general, the key diagnostic feature for hereditary spherocytosis (HS) and hereditary elliptocytosis (HE). However, in hereditary pyropoikilocytosis (HPP), the severe clinical form of HE, the morphological diagnosis is difficult due to the presence of a RBC morphological picture characterized by a mixture of elliptocytes, spherocytes, tear-drop cells, and fragmented cells. This difficulty increases in new-borns and/or patients requiring frequent transfusions, making impossible the prediction of the disease course or its severity. Recently, it has been demonstrated that the measurement of osmotic gradient ektacytometry (OGE), using a laser-assisted optical rotational ektacytometer LoRRca (MaxSis, RR Mechatronics), allows a clear differentiation between HS and HE, where the truncated osmoscan curve reflects the inability of the already elliptical cells to deform further under shear stress in the face of hypotonicity. In HPP, however, the RBCs appear to have a significantly decreased ability to maintain deformability in these conditions, and the classical trapezoidal profile of HE is less evident or indistinguishable from HS. Here, two unrelated patients with hereditary hemolytic anemia (HHA) due to HPP and HS, respectively, are described with the joint inheritance of a complex set of five genetic defects. Two of these defects are novel alpha-spectrin gene (SPTA1) variants, one is a microdeletion that removes the entire SPTA1 gene, and two are well-known low-expression polymorphic alleles: α-LELY and α-LEPRA. In the HPP patient (ID1), with many circulating spherocytes, the interactions between the two SPTA1 gene variants may lead, in addition to an elongation defect (elliptocytes), to a loss of membrane stability and vesiculation (spherocytes), and RBCs appear to have a significantly decreased ability to maintain deformability in hypotonic conditions. Due to this, the classical trapezoidal profile of HE may become less evident or indistinguishable from HS. The second patient (ID2) was a classical severe form of HS with the presence of more than 20% of spherocytes and few pincered cells. The severity of clinical manifestation is due to the coinheritance of a microdeletion of chromosome 1 that removes the entire SPTA1 gene with a LEPRA SPTA1 variant in trans. The diagnostic interest of both observations is discussed., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Red blood cell (RBC) populations are inherently heterogeneous, given mature RBC lack the transcriptional machinery to re-synthesize proteins affected during in vivo aging. Clearance of older, less functional cells thus aids in maintaining consistent hemorheological properties. Scenarios occur, however, where portions of mechanically impaired RBC are re-introduced into blood (e.g., damaged from circulatory support, blood transfusion) and may alter whole blood fluid behavior. Given such perturbations are associated with poor clinical outcomes, determining the tolerable level of abnormal RBC in blood is valuable. Thus, the current study aimed to define the critical threshold of blood fluid properties to re-infused physically-impaired RBC. Cell mechanics of RBC were impaired through membrane cross-linking (glutaraldehyde) or intracellular oxidation (phenazine methosulfate). Mechanically impaired RBC were progressively re-introduced into the native cell population. Negative alterations of cellular deformability and high shear blood viscosity were observed following additions of only 1-5% rigidified RBC. Low-shear blood viscosity was conversely decreased following addition of glutaraldehyde-treated cells; high-resolution microscopy of these mixed cell populations revealed decreased capacity to form reversible aggregates and decreased aggregate size. Mixed RBC populations, when exposed to supraphysiological shear, presented with compounded mechanical impairment. Collectively, key determinants of blood flow behavior are sensitive to mechanical perturbations in RBC, even when only 1-5% of the cell population is affected. Given this fraction is well-below the volume of rigidified RBC introduced during circulatory support or transfusion practice, it is plausible that some adverse events following surgery and/or transfusion may be related to impaired blood fluidity., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Sickle cell disease, a genetic disorder affecting a sizeable global demographic, manifests in sickle red blood cells (sRBCs) with altered shape and biomechanics. sRBCs show heightened adhesive interactions with inflamed endothelium, triggering painful vascular occlusion events. Numerous studies employ microfluidic-assay-based monitoring tools to quantify characteristics of adhered sRBCs from high resolution channel images. The current image analysis workflow relies on detailed morphological characterization and cell counting by a specially trained worker. This is time and labor intensive, and prone to user bias artifacts. Here we establish a morphology based classification scheme to identify two naturally arising sRBC subpopulations-deformable and non-deformable sRBCs-utilizing novel visual markers that link to underlying cell biomechanical properties and hold promise for clinically relevant insights. We then set up a standardized, reproducible, and fully automated image analysis workflow designed to carry out this classification. This relies on a two part deep neural network architecture that works in tandem for segmentation of channel images and classification of adhered cells into subtypes. Network training utilized an extensive data set of images generated by the SCD BioChip, a microfluidic assay which injects clinical whole blood samples into protein-functionalized microchannels, mimicking physiological conditions in the microvasculature. Here we carried out the assay with the sub-endothelial protein laminin. The machine learning approach segmented the resulting channel images with 99.1±0.3% mean IoU on the validation set across 5 k-folds, classified detected sRBCs with 96.0±0.3% mean accuracy on the validation set across 5 k-folds, and matched trained personnel in overall characterization of whole channel images with R2 = 0.992, 0.987 and 0.834 for total, deformable and non-deformable sRBC counts respectively. Average analysis time per channel image was also improved by two orders of magnitude (∼ 2 minutes vs ∼ 2-3 hours) over manual characterization. Finally, the network results show an order of magnitude less variance in counts on repeat trials than humans. This kind of standardization is a prerequisite for the viability of any diagnostic technology, making our system suitable for affordable and high throughput disease monitoring., Competing Interests: I have read the journal’s policy and the authors of this manuscript have the following competing interests: UAG and Case Western Reserve University have financial interests in BioChip Labs Inc. (Cleveland, Ohio). BioChip Labs Inc. offers commercial clinical microfluidic biomarker assays for inherited or acquired blood disorders. Financial interests include licensed intellectual property, stock ownership, research funding, employment, and consulting. UAG and Case Western Reserve University have financial interests in Xatek Inc. (Cleveland, Ohio). Xatek Inc. offers point-of-care global assays to evaluate the hemostatic process. Financial interests include licensed intellectual property and stock ownership. UAG and Case Western Reserve University have financial interests in Hemex Health Inc. (Portland, Oregon). Hemex Health Inc. offers point-of-care diagnostics for hemoglobin disorders, anemia, and malaria. Financial interests include licensed intellectual property, stock ownership, research funding, employment, and consulting. UAG has financial interests in DxNow Inc. (Gaithersburg, MD). DxNow Inc. offers microfluidic and bio-imaging technologies for in vitro fertilization, forensics, and diagnostics. Financial interests include licensed intellectual property and stock ownership. Competing interests of Case Western Reserve University employees are overseen and managed by the Conflict of Interests Committee according to a Conflict-of-Interest Management Plan. A patent application has been filed related to the methods discussed in this work.

Infantile pyknocytosis is a rare and self-limiting cause of hemolytic anemia in neonates. It can result in severe anemia and hyperbilirubinemia. The pathogenesis is unknown: a genetic origin has been discussed; however, based on the current literature it is not clear which genetic mutations should be considered. We present a case of a premature twin, in whom genetic screening was performed. Genetic mutations in 46 genes associated with hereditary hemolytic anemia and dyserythropoietic anemia were tested. No mutations were found. In infantile pyknocytosis, a genetic defect in these genes is unlikely., Competing Interests: The authors declare no conflict of interest., (Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.)

Schistocytosis is the morphological hallmark of the microangiopathic haemolytic anaemia of thrombotic microangiopathy (TMA). Consensus guidelines for manual schistocyte quantitation are available, but limited research has evaluated them. The 2012 International Council for Standardization in Haematology (ICSH) recommends a schistocyte quantitation of 1% as a robust cut-off for significance, with the quantitation including helmet, crescent, triangle and keratocyte poikilocytes; and microspherocytes only in the presence of helmets, crescents/triangles, and keratocytes. We aimed to evaluate the relative contribution of these different poikilocytes to schistocyte counting; compare the ICSH method with our proposed method which counts only cells most specific for red cell fragmentation (helmet, crescent and triangular schistocytes); and evaluate inter- and intra-observer agreement. Blood films were sourced from the Australian Snakebite Project, including non-envenomed and envenomed cases, with and without TMA. In blood films across the range of schistocytosis, the predominant poikilocytes present were helmets and crescents. Triangles, keratocytes and microspherocytes were typically only present when ICSH schistocyte count was >1%. With results dichotomised as <1.0% or ≥1.0%, our proposed new method versus the ICSH method showed almost perfect agreement [observed agreement 95%, Cohen's kappa (κ)=0.84, SE 0.04, 95% CI 0.76-0.92, p<0.005]. Inter-observer strength of agreement for our method was moderate (Fleiss' κ for comparisons between three non-unique microscopists κ=0.50, SE 0.05, 95% CI 0.41-0.59, p<0.005). Intra-observer reproducibility assessed in two microscopists ranged from substantial (Cohen's κ=0.71, SE 0.08, 95% CI 0.55-0.86, p<0.005) to borderline almost perfect agreement (Cohen's κ=0.81, SE 0.07, 95% CI 0.68-0.93, p<0.005). Schistocyte quantitation using our new method is simpler than the 2012 ICSH method and had almost perfect agreement. Our finding of moderate inter-observer agreement in quantitating helmet, triangle and crescent schistocytes is applicable to both the ICSH and our newly proposed method. This finding underscores the importance of clinicopathological correlation and repeated examinations in the context of a clinically suspected TMA., (Copyright © 2021 The Author(s). Published by Elsevier B.V. All rights reserved.)

Objective: Hepatic and biliary tract diseases are common in sickle cell disease (SCD) patients, likely due to sickling, hemosiderosis, viral hepatitis, or cholelithiasis. Literature is lacking on associations between SCD, autoimmune hepatitis (AIH), and/or sclerosing cholangitis (SC)-together, autoimmune liver disease (AILD). We aimed to better understand the relationship of these diseases in pediatric patients., Materials and Methods: A retrospective analysis of patients with SCD and AILD at the Children's Hospital of Philadelphia (January 2008 to August 2015)., Results: Seven patients, ages 8 to 23 years (3 males), were identified. Three had AIH, 2 SC, and 2 AIH/SC overlap, known as autoimmune SC. All patients with AIH treated with azathioprine significantly improved their liver enzymes. One patient with SC and inflammatory bowel disease underwent successful bone marrow transplant. Two SC patients died from SCD complications., Conclusions: In this cohort, there seems to be an association between SCD and AILD; SC in this population was severe. Physicians should be aware of this and evaluate patients with SCD and elevated liver enzymes for AILD., Competing Interests: The authors declare no conflict of interest., (Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.)

Hereditary red blood cell (RBC) membranopathies are characterized by mutations in genes encoding skeletal proteins that alter the membrane complex structure. Hereditary spherocytosis (HS) is the most common inherited RBC membranopathy leading to hereditary hemolytic anemia with a worldwide distribution and an estimated prevalence, in Europe, of about 1:2000 individuals. The recent availability of targeted next generation sequencing (t-NGS) and its combination with RBC deformability measured with a laser-assisted optical rotational ektacytometer (LoRRca) has demonstrated to be the most powerful contribution to lower the percentage of hereditary hemolytic anemia undiagnosed cases. In order to know the kind and frequency of RBC membrane mutations in our geographical area (Catalonia) and to better understand their pathophysiology, 42 unrelated, non-transfusion-dependent (NTD) patients with hereditary hemolytic anemia have been studied by combining t-NGS and LoRRca. The osmoscan module of LoRRca provides three rheological profiles that reflect the maximal deformability (EImax), osmotic fragility (Omin), and hydration state (Ohyper) of RBCs and contribute to a better understanding of the contribution RBC rheology to the severity of anemia. From the 42 patients studied, 37 were suspected to be a RBC membrane defect due to phenotypic characteristics and abnormal RBC morphology and, from these, in 31 patients (83.8% of cases) the mutation was identified by t-NGS. No definite diagnosis was achieved in 11 patients (26.2% of cases), including 6 out of 37 cases, with suspected membranopathy, and 5 with unclassifiable HHA. In all these undiagnosed patients, the existence of hemoglobinopathy and/or enzymopathy was ruled out by conventional methods.

The mechanical properties of erythrocytes have been investigated by different techniques. However, there are few reports on how the viscoelasticity of these cells varies during malaria disease. Here, we quantitatively map the viscoelastic properties of Plasmodium falciparum-parasitized human erythrocytes. We apply new methodologies based on optical tweezers to measure the viscoelastic properties and defocusing microscopy to measure the erythrocyte height profile, the overall cell volume, and its form factor, a crucial parameter to convert the complex elastic constant into complex shear modulus. The storage and loss shear moduli are obtained for each stage of parasite maturation inside red blood cells, while the former increase, the latter decrease. Employing a soft glassy rheology model, we obtain the power-law exponent for the storage and loss shear moduli, characterizing the soft glassy features of red blood cells in each parasite maturation stage. Ring forms present a liquid-like behavior, with a slightly lower power-law exponent than healthy erythrocytes, whereas trophozoite and schizont stages exhibit increasingly solid-like behaviors. Finally, the surface elastic shear moduli, low-frequency surface viscosities, and shape recovery relaxation times all increase not only in a stage-dependent manner but also when compared to healthy red blood cells. Overall, the results call attention to the soft glassy characteristics of Plasmodium falciparum-parasitized erythrocyte membrane and may provide a basis for future studies to better understand malaria disease from a mechanobiological perspective., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Tubular aggregate myopathy (TAM) is a progressive disorder characterized by muscle weakness, cramps, and myalgia. TAM clinically overlaps with Stormorken syndrome (STRMK), combining TAM with miosis, thrombocytopenia, hyposplenism, ichthyosis, short stature, and dyslexia. TAM and STRMK arise from gain-of-function mutations in STIM1 (stromal interaction molecule 1) or ORAI1, both encoding key regulators of Ca 2+ homeostasis, and mutations in either gene result in excessive extracellular Ca 2+ entry. The pathomechanistic similarities and differences between TAM and STRMK are only partially understood. Here we provide functional in vitro experiments demonstrating that STIM1 harboring the TAM D84G or the STRMK R304W mutation similarly cluster and exert a dominant effect on the wild-type protein. Both mutants recruit ORAI1 to the clusters, increase cytosolic Ca 2+ levels, promote major nuclear import of the Ca 2+ -dependent transcription factor NFAT (nuclear factor of activated T cells), and trigger the formation of circular membrane stacks. In conclusion, the analyzed TAM and STRMK mutations have a comparable impact on STIM1 protein function and downstream effects of excessive Ca 2+ entry, highlighting that TAM and STRMK involve a common pathomechanism., (© 2020 Japanese Society of Neuropathology.)

Objectives: Hereditary elliptocytosis (HE) is inherited in an autosomal dominant fashion, and the majority of HE-associated defects occur due to qualitative and quantitative defects in the RBC membrane skeleton proteins α-spectrin, β-spectrin, or protein 4.1R. The complex EPB41 gene encodes a diverse family of protein 4.1R isoforms which are key components of the erythroid membrane skeleton that regulates red cell morphology and mechanical stability. The purpose of this study was to investigate the genome of a Korean patient with HE to discover the causative gene mutation using gene panel sequencing. Methods: An 89-year-old female presented to the Emergency Department and was diagnosed with pancreatitis and gallstones. A peripheral blood smear revealed that approximately 60% of the RBCs were abnormally shaped and appeared oval or elongated, from slightly egg-shaped to rod or pencil forms (elliptocytes). Targeted gene panel sequencing consisting of 33 genes related to inherited RBC disorders and Sanger sequencing were performed. Results: A heterozygous c.2112G > A of the EPB41 gene leading to premature termination codon (NM&#95;001166005.1:c.2112G > A, p.Trp704*) was identified. This variant, which had not been previously reported to be related to HE, was confirmed by Sanger sequencing. Thus, the patient's diagnosis of HE-1 was genetically confirmed. Conclusion: The present study confirmed a novel mutation of the EPB41 gene that plays an important role in expanding the mutational distribution in HE-1. It could also be helpful for understanding the correlation between the genotype and phenotype in HE.

Chronic hemolysis, enhanced oxidative stress, and decreased nitric oxide (NO) bioavailability promote vasculopathy in sickle cell anemia (SCA). Oxidative stress and NO are known to modulate eryptosis in healthy red blood cells (RBCs); however, their role in SCA eryptosis and their impact on the genesis of RBC-derived microparticles (RBC-MPs) remains poorly described. RBC-MPs could play a role in vascular dysfunction in SCA. The aims of this study were to evaluate the roles of oxidative stress and NO in eryptosis and RBC-MPs release, and to determine whether RBC-MPs could be involved in vascular dysfunction in SCA. Markers of eryptosis and oxidative stress, plasma RBC-MPs concentration and arterial stiffness were compared between SCA and healthy (AA) individuals . In-vitro experiments were performed to test: 1) the effects of oxidative stress (antioxidant: n-acetylcysteine (NAC); pro-oxidant: cumene hydroperoxide) and NO (NO donor: sodium nitroprusside (SNP); NO-synthase inhibitor (L-NIO)) on eryptosis, RBC deformability and RBC-MP genesis; 2) the effects of SCA/AA-RBC-MPs on human aortic endothelial cell (HAEC) inflammatory phenotype and TLR4 pathway. Eryptosis, RBC-MPs, oxidative stress and arterial stiffness were increased in SCA. NAC increased RBC deformability and decreased eryptosis and RBC-MPs release, while cumene did the opposite. SNP increased RBC deformability and limited eryptosis, but had no effect on RBC-MPs. L-NIO did not affect these parameters. Arterial stiffness was correlated with RBC-MPs concentration in SCA. RBC-MPs isolated directly from SCA blood increased adhesion molecules expression and the production of cytokines by HAEC compared to those isolated from AA blood. TLR4 inhibition alleviated these effects. Our data show that oxidative stress could promote eryptosis and the release of RBC-MPs that are potentially involved in macrovascular dysfunction in SCA., (Copyright © 2020 Nader, Romana, Guillot, Fort, Stauffer, Lemonne, Garnier, Skinner, Etienne-Julan, Robert, Gauthier, Cannas, Antoine-Jonville, Tressières, Hardy-Dessources, Bertrand, Martin, Renoux, Joly, Grau and Connes.)

The mature red blood cell (RBC) lacks a nucleus and organelles characteristic of most cells, but it is elegantly structured to perform the essential function of delivering oxygen and removing carbon dioxide from all other cells while enduring the shear stress imposed by navigating small vessels and sinusoids. Over the past several decades, the efforts of biochemists, cell and molecular biologists, and hematologists have provided an appreciation of the complexity of RBC membrane structure, while studies of the RBC membrane disorders have offered valuable insights into structure-function relationships. Within the last decade, advances in genetic testing and its increased availability have made it possible to substantially build upon this foundational knowledge. Although disorders of the RBC membrane due to altered structural organization or altered transport function are heterogeneous, they often present with common clinical findings of hemolytic anemia. However, they may require substantially different management depending on the underlying pathophysiology. Accurate diagnosis is essential to avoid emergence of complications or inappropriate interventions. We propose an algorithm for laboratory evaluation of patients presenting with symptoms and signs of hemolytic anemia with a focus on RBC membrane disorders. Here, we review the genotypic and phenotypic variability of the RBC membrane disorders in order to raise the index of suspicion and highlight the need for correct and timely diagnosis., (© 2020 by The American Society of Hematology.)

Hb Manitoba [α102(G9)Ser→Arg] results from an A GC> C GC or AG C >AG A substitution at codon 102 of the HBA1 or HBA2 genes. The variant is mildly unstable but carriers typically have normal clinical presentation and hematological profile. Hb Manitoba has not been reported in Pasifika of Tongan, Samoan or New Zealand (NZ) Māori descent before. The cases presented here support the findings from existing literature but include results from alternative methodology including capillary zone electrophoresis (CZE), which may slightly underestimate the true variant percentage. The subject of our case report, a Tongan male with microcytic indices, was shown to be heterozygous for Hb Manitoba III ( HBA2 : c.309C>A) coinherited with the -α 3.7 (rightward) deletion.

Sickle cell disease (SCD) is a monogenic red blood cell (RBC) disorder with high morbidity and mortality. Here, we report, for the first time, the impact of SCD on the bone marrow (BM) vascular niche, which is critical for hematopoiesis. In SCD mice, we find a disorganized and structurally abnormal BM vascular network of increased numbers of highly tortuous arterioles occupying the majority of the BM cavity, as well as fragmented sinusoidal vessels filled with aggregates of erythroid and myeloid cells. By in vivo imaging, sickle and control RBCs have significantly slow intravascular flow speeds in sickle cell BM but not in control BM. In sickle cell BM, we find increased reactive oxygen species production in expanded erythroblast populations and elevated levels of HIF-1α. The SCD BM exudate exhibits increased levels of proangiogenic growth factors and soluble vascular cell adhesion molecule-1. Transplantation of SCD mouse BM cells into wild-type mice recapitulates the SCD vascular phenotype. Our data provide a model of SCD BM, in which slow RBC flow and vaso-occlusions further diminish local oxygen availability in the physiologic hypoxic BM cavity. These events trigger a milieu that is conducive to aberrant vessel growth. The distorted neovascular network is completely reversed by a 6-week blood transfusion regimen targeting hemoglobin S to <30%, highlighting the plasticity of the vascular niche. A better insight into the BM microenvironments in SCD might provide opportunities to optimize approaches toward efficient and long-term hematopoietic engraftment in the context of curative therapies., (© 2020 by The American Society of Hematology.)

Sickle cell disease (SCD) is an autosomal recessive blood disorder which occurs due to point mutation in the β-globin chain of hemoglobin. Since the past decades, various therapies have been put forth, which are based on obstructing pathophysiological mechanisms of SCD including inhibition of Gardos channel and cation fluxes which in turn prevents sickle erythrocyte destruction and dehydration. The pharmacological approaches are based on the mechanism of reactivating γ-globin expression by utilizing fetal hemoglobin (HbF)-inducing drugs such as hydroxyurea. In SCD, gene therapy could be considered as a promising tool which involves modifying mutation at the gene-specific target by either promoting insertion or deletion of globins. Although there are various therapies emerged so far in the treatment of SCD, many of them have faced a major setback in most of developing countries in terms of cost, unavailability of expertise, and suitable donor. Therefore, in addition to pathophysiological aspects, this review will discuss new advancements and approaches made in the therapeutic domain of SCD including a viewpoint of modulating hemoglobin in SCD by the intervention of probiotics.

Background: Congenital dyserythropoiesis anemia type Ia (OMIM:224120), is a rare hereditary anemia. The diagnosis is difficult to make and usually delayed in part due to its rarity and nonspecific clinical manifestations., Methods: Whole exome sequencing was applied for the genetic diagnosis of a 12-year-old boy who has suffered from hemolytic anemia since birth and who requires regular transfusions. Sanger sequencing of the variants detected in whole exome sequencing was performed in the patient and his parents., Results: Compound heterozygous mutations of CDAN1 gene, including one previously reported and one novel mutation, which is a splicing change, were detected in the whole exome sequencing and confirmed by Sanger sequencing. The autosomal recessive inheritance was confirmed by pedigree analysis., Conclusion: To our knowledge, this is the first case report of congenital dyserythropoiesis anemia type Ia with genetic diagnosis to be located in Taiwan. Because of the rarity of CDA Ia and the overlapping of the clinical manifestations with other hereditary anemias, the next-generation sequencing approach is effective for conclusive diagnosis of CDA Ia., (© 2020 The Authors. Molecular Genetics & Genomic Medicine published by Wiley Periodicals, Inc.)

Introduction: Early detection of endothelial graft-vs-host disease (GVHD) after hematopoietic stem cell transplantation (HSCT) might help protect the patient from the late and severe complications of transplant-associated thrombotic microangiopathy (TA-TMA). Appearance of schistocytes in peripheral blood is one of the cardinal diagnostic features of TA-TMA. Our aim was to test the diagnostic accuracy and objectiveness of digital microscopy with respect to the recognition and quantification of schistocytes in the setting of endothelial GVHD., Methods: Peripheral blood smears from 127 allogeneic and 63 autologous HSCT patients (January 2016-June 2017) were retrospectively examined before, 1 month and at 2-3 months after transplantation using digital microscopy. Peripheral blood smears from 31 healthy blood donors were also analyzed as the control group., Results: Assessment by digital microscopy showed that schistocytes are significantly increased after 3 months from the allogeneic (P < .001) or the autologous HSCT (P < .001) compared to the control group. Significantly higher schistocyte counts were found in patients with acute GVHD (P = .05) and in patients with HLA mismatch (P = .005). Patients in the upper quartile of the schistocyte counts had significantly more frequently acute GVHD (P = .024) or HLA mismatch (P = .035)., Conclusions: Schistocytes can be reliably counted by means of a digital microscopy system and are significantly higher in patients with acute GVHD and HLA mismatch. Inversely, patients with the highest numbers of schistocytes are more frequently affected by aGVHD, implying that high schistocyte counts after HSCT might be a surrogate marker for this complication., (© 2019 John Wiley & Sons Ltd.)

Sickle cell anemia (SCA) is associated with morbidity and early death. While the switch from fetal to sickle hemoglobin during the first months of life results in hemolytic anemia with reticulocytosis, the role of the reticulocyte in the pathophysiology and prognosis of SCA is not well-defined. Reticulocytes have unique cytoskeletal and membrane components that allow them to be distinguished from mature sickle erythrocytes in the circulation. Reticulocytes in patients with SCA are less dense than more mature and 'sickled' erythrocytes, and have increased adhesive properties. The circulating reticulocyte number in peripheral blood may assist in predicting disease severity in SCA; characterization of patient-specific reticulocyte properties during infancy and childhood may assist in predicting therapeutic response to therapies. Here, we review the biological and clinical data regarding reticulocytes and their potential impact on SCA pathophysiology and disease severity., Competing Interests: Declaration of Competing Interest The authors declare no competing financial interests., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Hereditary xerocytosis (HX) is a rare, autosomal dominant congenital hemolytic anemia (CHA) characterized by erythrocyte dehydration with presentation of various degrees of hemolytic anemia. HX is often misdiagnosed as hereditary spherocytosis or other CHA. Here we report three cases of suspected HX and one case of HX associated with β-thalassemia. Sanger method was used for sequencing cDNA of the PIEZO1 gene. Variants were evaluated for potential pathogenicity by MutationTaster, PROVEAN, PolyPhen-2 and M-CAP software, and by molecular modeling. Four different variants in the PIEZO1 gene were found, including three substitutions (p.D669H, p.D1566G, p.T1732 M) and one deletion (p.745delQ). In addition, in the patient with the p.T1732 M variant we detected a 12-nucleotide deletion in the β-globin gene leading to a deletion of amino acids 62AHGK65. The joint presence of mutations in two different genes connected with erythrocytes markedly aggravated the presentation of the disease. Bioinformatic analysis and molecular modeling strongly indicated likely deleterious effects of all four PIEZO1 variants, but co-segregation analysis showed that the p.D1566G substitution is in fact non-pathogenic. Identification of causative mutations should improve the diagnosis and management of HX and provide a new insight into the molecular basis of this complex red blood cell abnormality., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Objectives : Hematopoietic stem cell transplantation (HSCT)-associated thrombotic microangiopathy (TA-TMA) is an important early post-treatment condition. This study evaluated the Revised %MICRO, a parameter obtained from the ADVIA 2120i automated blood cell counter, as a surrogate marker of the schistocyte ratio. We hypothesized that individual differences between the %MICRO value and schistocyte ratio would remain constant. Design and Methods: EDTA-2K-treated peripheral blood samples were collected from 19 patients who underwent allogeneic HSCT from April 2014 to September 2018. First, the baseline difference, X, was calculated using a sample from the first day after HSCT as X = %MICRO (first day) - schistocyte ratio (first day). Next, the Revised %MICRO for each subsequent day was calculated as Revised %MICRO = %MICRO - X. We evaluated correlations of the schistocyte ratio with the calculated %MICRO and Revised %MICRO and the RBC fragment, RBC distribution width, %MICRO and Revised %MICRO data obtained from the ADVIA 2120i. Results : The mean schistocyte percentage and Revised %MICRO were both 0.4% ± 0.6. RBC fragments correlated weakly with the %MICRO and schistocyte ratio, respectively (r = 0.162 and r = 0.771, respectively), whereas the Revised %MICRO correlated strongly with the schistocyte ratio (r = 0.893). Conclusion : The Revised %MICRO appears to be a good surrogate of the schistocyte ratio in a clinical setting. J. Med. Invest. 67 : 250-254, August, 2020.

In sickle cell disease (SCD), a single point mutation in the gene coding for beta-globin causes the production of abnormal hemoglobin S (HbS). When deoxygenated, HbS can polymerize, forming rigid rods of hemoglobin, resulting in the sickling of red blood cells (RBCs). These sickled RBCs have significantly reduced deformability, causing vaso-occlusion, which leads to numerous SCD-related clinical complications, including pain, stroke, and organ damage. RBC deformability is also reduced by RBC dehydration, resulting in dense red blood cells that are more likely to sickle. To date, there is not a single widely available, rapid, and reproducible laboratory assay capable of predicting the disease severity or directly monitoring the treatment effects for novel, non-fetal hemoglobin inducing therapies. In this study, we describe a protocol to measure RBC deformability as a function of pO2 that allows for the quantitation of sickling behavior in SCD patients. Oxygen gradient ektacytometry measures RBC deformability, expressed as the elongation index (EI), as a function of pO2. RBCs are exposed to a fixed shear stress of 30 Pa during one round of deoxygenation and reoxygenation. Six readout parameters are produced. Of these, the point of sickling (PoS), defined as the pO2 at which maximum EI (EImax) shows a 5% decrease, and minimum EI during deoxygenation (EImin) are the most informative, reflecting an individual patient's pO2 at which sickling starts and the minimal deformability of a patient's red blood cells, respectively. PoS is associated with an individual patient's hemoglobin affinity for oxygen, whereas EImin shows a strong correlation with fetal hemoglobin levels. We conclude that oxygen gradient ektacytometry is a promising technique to monitor the treatment of patients with SCD, as a biomarker for anti-sickling agents in clinical and preclinical trials, and an important tool to study sickling behavior of RBCs from individuals with SCD and sickle cell traits.

Hereditary spherocytosis (HS) is characterised by increased osmotic fragility and enhanced membrane loss of red blood cells (RBC) due to defective membrane protein complexes. In our diagnostic laboratory, we observed that pyruvate kinase (PK) activity in HS was merely slightly elevated with respect to the amount of reticulocytosis. In order to evaluate whether impaired PK activity is a feature of HS, we retrospectively analysed laboratory data sets from 172 unrelated patients with HS, hereditary elliptocytosis (HE), glucose-6-phosphate dehydrogenase (G6PD) or PK deficiency, sickle cell or haemoglobin C disease, or β-thalassaemia minor. Results from linear regression analysis provided proof that PK activity decreases with rising reticulocyte counts in HS (R 2  = 0·15; slope = 9·09) and, less significantly, in HE (R 2  = 0·021; slope = 8·92) when compared with other haemolytic disorders (R 2  ≥ 0·65; slopes ≥ 78·6). Reticulocyte-adjusted erythrocyte PK activity levels were significantly lower in HS and even declined with increasing reticulocytes (R 2  = 0·48; slope = -9·74). In this report, we describe a novel association between HS and decreased PK activity that is apparently caused by loss of membrane-bound PK due to impaired structural integrity of the RBC membrane and may aggravate severity of haemolysis in HS., (© 2019 British Society for Haematology and John Wiley & Sons Ltd.)

Cell sickling is the process in which intracellular polymerization of deoxygenated sickle hemoglobin (HbS) leads to distorted, rigid cells, resulting in abnormal blood rheology and painful vaso-occlusion. Current methods for detection of this process mainly rely on optical microscopy of cellular morphology and measurements of cell deformability and blood rheology. As electrical impedance of cells is a sensitive indicator of changes in cellular structure and biophysical characteristics, it can be a promising marker for characterization of abnormal blood rheology and a means more convenient than optics to be integrated into point-of-care devices. In this work, a microfluidics-based electrical impedance sensor has been developed for characterizing the dynamic cell sickling-unsickling processes in sickle blood. The sensor is capable of measuring the continuous variation in the sickle cell suspension due to cyclic hypoxia-induced intracellular HbS polymerization and depolymerization. Simultaneous microscopic imaging of cell morphological change shows the reliability and repeatability of the electrical impedance-based measurements of cell sickling and unsickling processes. Strong correlation is found between the electrical impedance measurement and patients' hematological parameters such as levels of HbS and fetal hemoglobin. The combination of electrical impedance measurement and on-chip hypoxia control provides a promising method for rapid assessment of the dynamic processes of cell sickling and unsickling in patients with sickle cell disease.

Elevated fetal hemoglobin (HbF) is associated with reduced severity of sickle cell disease. Therefore, γ-globin protein levels and F-cell (HbF-positive red blood cell) percentages are used for estimation of clinical benefit. Here, we monitored transplantation-related changes in HbF and F-cell percentages for rhesus macaques (Macaca mulatta) following total body irradiation or busulfan conditioning prior to CD34 + cell transplantation. HbF protein expression peaked in the first 4-9 weeks posttransplant (0.99%-2.53%), and F-cells increased in the first 6-17 weeks posttransplant (8.7%-45.3%). HbF and F-cell ratios gradually decreased and stabilized to levels similar to those of control animals (1.96 ± 1.97% for F cells and 0.49 ± 0.19% γ-globin expression) 4-7 months post-transplant. These findings confirm and expand on previous reports of transient induction in HbF and F-cell percentages in rhesus macaques following CD34 + cell transplantation, an observation that must be taken into consideration when evaluating therapeutic strategies that aim to specifically elevate HbF expression, which are currently in clinical development., (Published by Elsevier Inc.)

Sickle cell disease (SCD) is associated with chronic activation of coagulation and an increased risk of venous thromboembolism. Erythrocyte sickling, the primary pathologic event in SCD, results in dramatic morphological changes in red blood cells (RBCs) because of polymerization of the abnormal hemoglobin. We used a mouse model of SCD and blood samples from sickle patients to determine if these changes affect the structure, properties, and dynamics of sickle clot formation. Sickling of RBCs and a significant increase in fibrin deposition were observed in venous thrombi formed in sickle mice. During ex vivo clot contraction, the number of RBCs extruded from sickle whole blood clots was significantly reduced compared with the number released from sickle cell trait and nonsickle clots in both mice and humans. Entrapment of sickled RBCs was largely factor XIIIa-independent and entirely mediated by the platelet-free cellular fraction of sickle blood. Inhibition of phosphatidylserine, but not administration of antisickling compounds, increased the number of RBCs released from sickle clots. Interestingly, whole blood, but not plasma clots from SCD patients, was more resistant to fibrinolysis, indicating that the cellular fraction of blood mediates resistance to tissue plasminogen activator. Sickle trait whole blood clots demonstrated an intermediate phenotype in response to tissue plasminogen activator. RBC exchange in SCD patients had a long-lasting effect on normalizing whole blood clot contraction. Furthermore, RBC exchange transiently reversed resistance of whole blood sickle clots to fibrinolysis, in part by decreasing platelet-derived PAI-1. These properties of sickle clots may explain the increased risk of venous thromboembolism observed in SCD., (© 2019 by The American Society of Hematology.)