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TTP is a life-threatening disorder diagnosed using a combination of clinical information and laboratory results. ADAMTS13 activity and antibody testing represent a major advance in the field, but results can sometimes be difficult to interpret due to technical aspects of the tests and characteristics of the causative antibodies in acquired TTP. Genetic testing for ADAMTS13 mutations is also now available to assist with the diagnosis of inherited TTP. This review will focus on ADAMTS13 testing and will highlight patient and laboratory aspects that can lead to diagnostic difficulty. The effects of TTP therapies on test results will also be discussed.

International audience; Background: Thrombotic thrombocytopenic purpura (TTP) is a life‐threatening thrombotic microangiopathy (TMA) caused by a severe functional deficiency in ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type I repeats‐13), the specific von Willebrand factor (VWF) cleaving protease. ADAMTS13 activity is essential to diagnose TTP but remains challenging to assess, as reference ADAMTS13 activity assays are manual and time consuming. Current techniques also lack robustness in low detectable ADAMTS13 activity range, which could prove problematic for therapy‐driven monitoring.Objectives: The HemosIL AcuStar ADAMTS13 activity assay is a fast, automated chemiluminescent assay, the performance of which remains to be evaluated prospectively on very large cohorts of patients with TMA and in real‐life conditions.Patients and Methods: Our study was conducted over two successive sequences: a retrospective evaluation followed by a “real‐life” prospective evaluation. Overall, we evaluated the HemosIL AcuStar ADAMTS13 activity assay on 539 citrated plasma samples. We extensively studied linearity, limit of detection, contamination, intra‐assay and interassay precisions with a specific focus on levels < 25 IU/dL. Diagnostic performances for the detection of < 10 IU/dL ADAMTS13 activity and overall method comparison were conducted with the fluorescence resonance energy transfer (FRETS)‐VWF73 assay as the reference method.Results: Technical performance proved excellent. Robustness in low detectable ADAMTS13 activity range was good, potentially qualifying this assay for therapy‐driven monitoring. Comparison with the FRETS‐VWF73 assay was satisfactory (r2 = .83, P < .0001) as were the diagnostic performances for acute‐phase TTP (specificity, 99.7%; positive predictive value, 99.2%).Conclusion: The HemosIL AcuStar ADAMTS13 activity assay is a fast, reliable, automated technique well adapted as a first‐line ADAMTS13 activity assay for TTP diagnosis and follow‐up.

BACKGROUND Prediction of HAIC treatment response is important for improving the prognosis in patients with hepatocellular carcinoma (HCC). The progression of HCC is related to hypercoagulability and angiogenesis. It is known that ADAMTS13 and von Willebrand factor (VWF) are related to hypercoagulability. In addition, previous study reported that the association between ADAMTS13 and VWF, and angiogenesis via vascular endothelial growth factor (VEGF). Recently, ADAMTS13 and VWF have been associated with the prognosis in patients with various kinds of cancer undergoing chemotherapy. AIM To investigate whether ADAMTS13 and VWF become useful biomarkers of treatment response in HCC patients before the initiation of HAIC treatment. METHODS Seventy-two patients were enrolled in this study. ADAMTS13 activity (ADAMTS13:AC), VWF antigen (VWF:Ag) and VEGF levels were determined via enzyme-linked immunosorbent assay. Univariable and multivariable analyses were performed to determine the predictive factors of treatment response in patients with HCC undergoing HAIC treatment. RESULTS ADAMTS13:AC levels in HCC patients with stable disease (SD) + partial response (PR) of HAIC treatment were significantly higher than those with progressive disease (PD) (P < 0.05). In contrast, VWF:Ag/ADAMTS13:AC ratio and VEGF levels in HCC patients with SD + PR were significantly lower than those with PD (both P < 0.05). Patients with high VWF:Ag/ADAMTS13:AC ratio (> 2.7) had higher VEGF levels than those with low ratio (≤ 2.7). Multivariable analysis revealed that VWF:Ag/ADAMTS13:AC ratio was a predictive factor of HAIC treatment response. CONCLUSION VWF:Ag/ADAMTS13:AC ratio may become a useful biomarker of treatment response in HCC patients before the initiation of HAIC treatment.

The Hereditary TTP Registry is an international cohort study for patients with a confirmed or suspected diagnosis of hereditary thrombotic thrombocytopenic purpura (hTTP) and their family members. Hereditary TTP is an ultra-rare blood disorder (prevalence of ∼1–2 cases per million), the result of autosomal-recessively inherited congenital ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) deficiency (ADAMTS13 activity

Background Despite advances in treatment options for thrombotic thrombocytopenic purpura (TTP), there are still limited high quality data to inform clinicians regarding its appropriate treatment. Methods In June 2018, the ISTH formed a multidisciplinary guideline panel to issue recommendations about treatment of TTP. The panel discussed 12 treatment questions related to immune-mediated TTP (iTTP) and hereditary or congenital TTP (cTTP). The panel used the Grading of Recommendations Assessment, Development, and Evaluation approach, including evidence-to-decision frameworks, to appraise evidence and formulate recommendations. Results The panel agreed on 11 recommendations based on evidence ranging from very low to moderate certainty. For first acute episode and relapses of iTTP, the panel made a strong recommendation for adding corticosteroids to therapeutic plasma exchange (TPE) and a conditional recommendation for adding rituximab and caplacizumab. For asymptomatic iTTP with low plasma ADAMTS13 activity, the panel made a conditional recommendation for the use of rituximab outside of pregnancy, but prophylactic TPE during pregnancy. For asymptomatic cTTP, the panel made a strong recommendation for prophylactic plasma infusion during pregnancy, and a conditional recommendation for plasma infusion or a wait and watch approach outside of pregnancy. Conclusions The panel's recommendations are based on all the available evidence for the effects of an individual component of various treatment approaches, including suppressing inflammation, blocking platelet clumping, replacing the missing and/or inhibited ADAMTS13, and suppressing the formation of ADAMTS13 autoantibody. There was insufficient evidence for further comparing different treatment approaches (eg, TPE, corticosteroids, rituximab, and caplacizumab, etc.), for which high quality studies are needed.

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening thrombotic microangiopathy caused by severely reduced activity of the von-Willebrand factor-cleaving protease ADAMTS13, mainly caused by anti-ADAMTS-13 antibodies. Although several test systems for ADAMTS13 measurement exist, long turn-around times hamper the usability in daily practice. We performed a method comparison study for two commercially available ADAMTS13 assays and evaluated the agreement between the fully-automated rapid turn-over HemosIL AcuStar ADAMTS13 Activity assay and the manually performed TECHNOZYM ADAMTS-13 Activity assay. Twenty-four paired test samples derived from 10 consecutively recruited patients (n = 8, acquired TTP; n = 1, atypical hemolytic uremic syndrome; n = 1, control), of which nine test samples were collected in case of clinically apparent TTP and 13 samples were collected from TTP patients in clinical remission were included. Overall correlation between the TECHNOZYM and AcuStar assay was good with a Pearson R of 0.93 (p or

The efficiency of von Willebrand factor (VWF) in thrombus formation is related to its multimeric size, which is controlled by the protease ADAMTS13. However, it is not clear what regulates ADAMTS13 activity. In this study, we investigated whether PF4 could bind to VWF and inhibit ADAMTS13 activity. We found that PF4 binds to VWF and protects against ADAMTS13 activity. We also found that VWF-PF4 complexes circulate in patients with thrombotic thrombocytopenic purpura (TTP). Our data provides the first evidence that PF4 may have a novel role in regulating VWF multimers during primary haemostasis and thrombosis.

COPD exacerbation; Coagulation; Cross-linked fibrin degradation Exacerbación de la EPOC; Coagulación; Degradación de fibrina reticulada Exacerbació de la MPOC; Coagulació; Degradació de fibrina reticulada Cardiovascular diseases are common in patients with chronic obstructive pulmonary disease (COPD). Clot formation and resolution secondary to systemic inflammation may be a part of the explanation. The aim was to determine whether biomarkers of clot formation (products of von Willebrand Factor formation and activation) and clot resolution (product of fibrin degeneration) during COPD exacerbation predicted major cardiovascular events (MACE). The cohort was based on clinical data and biobank plasma samples from a trial including patients admitted with an acute exacerbation of COPD (CORTICO-COP). Neo-epitope biomarkers of formation and the activation of von Willebrand factor (VWF-N and V-WFA, respectively) and cross-linked fibrin degradation (X-FIB) were assessed using ELISAs in EDTA plasma at the time of acute admission, and analyzed for time-to-first MACE within 36 months, using multivariable Cox proportional hazards models. In total, 299/318 participants had samples available for analysis. The risk of MACE for patients in the upper quartile of each biomarker versus the lower quartile was: X-FIB: HR 0.98 (95% CI 0.65–1.48), VWF-N: HR 1.56 (95% CI 1.07–2.27), and VWF-A: HR 0.78 (95% CI 0.52–1.16). Thus, in COPD patients with an acute exacerbation, VWF-N was associated with future MACE and warrants further studies in a larger population. This study was funded by the Danish Regions Medical Fund (grant no. 5894/16), the Danish Council for Independent Research (grant no. 6110-00268B), and the Novo Nordisk foundation (grant no. NNF20OC0060657). Author D.D.M. received personal funding from the Danish National Research Foundation (DNRF126).

Thrombotic thrombocytopenic purpura (TTP) is a rare thrombotic microangiopathy (TMA) characterized by the severe deficiency of a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13) activity (< 10%). Rapid ADAMTS13 testing is crucial for an early diagnosis and optimal management of acute TTP. We evaluated the performance of the HemosIL AcuStar ADAMTS13 activity assay (Instrumentation Laboratory, Bedford, Massachusetts, United States), a fully automated chemiluminescent immunoassay with an analytical time of 33 minutes. A method comparison study was performed on 176 samples from 49 healthy donors and 127 TMA patients (109 TTP, 7 atypical hemolytic uremic syndrome, 11 other TMAs), comparing this new assay with an in-house FRETS-VWF73 assay and a commercial enzyme-linked immunosorbent assay (ELISA) (TECHNOZYM ADAMTS-13 Activity, Technoclone GmbH, Vienna, Austria). Agreement between methods was assessed with focus on ADAMTS13 activity less than 10%, the medical decision level relevant for TTP diagnosis. The HemosIL AcuStar ADAMTS13 Activity showed good correlation with both the FRETS-VWF73 (r = 0.96) and ELISA (r = 0.96) methods. Slope of the Passing–Bablok regression was 1.05 for FRETS-VWF73 and 1.02 for ELISA, and absolute bias at the medical decision level was +0.1 and +0.3%, respectively. The study also revealed high agreement with FRETS-VWF73 (kappa 0.97) and ELISA (kappa 0.98) methods in classifying TTP patients with a severe deficiency of ADAMTS13 activity. Because of its short turnaround time and full automation, the HemosIL AcuStar ADAMTS13 activity assay might become the assay of choice to rapidly test ADAMTS13 activity in plasma and thus establish the diagnosis of acute TTP in emergency settings.

Background: Thrombotic thrombocytopenic purpura (TTP) is a potentially fatal disease that requires early diagnosis and treatment that can be made possible by applying the PLASMIC score. This study aims to evaluate this score applicability for patients with suspected TTP in a developing country. Methods: This was a retrospective study performed at a tertiary hospital in the northeastern region of Brazil. Patients were analyzed in two groups: ADAMTS13 activity 10%. Patients were stratified according to the PLASMIC score, and the level of agreement between the PLASMIC score and the ADAMTS13 activity was evaluated. Results: Eight patients with thrombotic microangiopathy were included. Four patients had ADAMTS13 activity 10%, all with a score

Objectives: This study aimed to investigate the association between plasma von Willebrand factor (VWF) level, ADAMTS13 activity, and neuroimaging features of cerebral small vessel disease (CSVD), including the CSVD neuroimaging markers and the overall CSVD burden.Methods: CSVD patients admitted to our hospital from 2016 to 2020 were recruited. Plasma VWF level and ADAMTS13 activity were measured. The overall effect of CSVD on the brain was described as a validated CSVD score. We evaluated the association between VWF levels, ADAMTS13 activity, and the increasing severity of CSVD score by the logistic regression model.Results: We enrolled 296 patients into this study. The mean age of the sample was 69.0 years (SD 7.0). The mean VWF level was 1.31 IU/mL, and the ADAMTS13 activity was 88.01 (SD 10.57). In multivariate regression analysis, lower ADAMTS13 activity and higher VWF level was related to white matter hyperintensity (WMH) [β = −7.31; 95% confidence interval (CI) (−9.40, −4.93); pβ = 0.17; 95% confidence interval (0.11, 0.23); pβ = −9.22; 95% CI (−11.37, −7.06); pβ = 0.21; 95% confidence interval (0.15, 0.27); pp = 0.22); β = 0.02; 95% confidence interval (−0.05, 0.08); p = 0.63]. Furthermore, ADAMTS13 activity was independently negatively correlated with the overall CSVD burden (odd ratio = 21.33; 95% CI (17.46, 54.60); p < 0.01) after adjustment for age, history of hypertension, and current smoking.Conclusions: Reducing ADAMTS13 activity change is related to white matter hyperintensity, subcortical infarction, but not with cerebral microhemorrhage. In addition, ADAMTS13 may have played an essential role in the progression of CSVD.

Systemic inflammation and coagulopathy are characteristic hallmarks of COVID19. “COVID coagulopathy” manifests mainly as a prothrombotic state affecting both large and small blood vessels, and presenting as arterial, venous, and microangiopathic thrombotic events with von Willebrand factor (VWF) and soluble thrombomodulin increased in hospitalized patients. The causes of coagulopathy are poorly understood. Aim: To investigate the relationship between von Willebrand factor (VWF) biomarkers, intravascular hemolysis, coagulation, and organ damage in COVID19 patients and to study their association with disease severity and mortality. Methods: 181 hospitalized adult COVID19 patients were randomly selected with a balanced distribution of survivors and non-survivors during the period of March 26th 2020 to May 5th 2020. The medical records and laboratory values were reviewed. Statistical analysis was performed using R studio V.3.6.2. Results: Patients who died (n=90) had significantly lower ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) activity, elevated lactate dehydrogenase levels, increased schistocyte/RBC fragment counts, and elevated VWF antigen and activity levels compared to patients discharged alive (n=91). In 31 patients, we measured several of these biomarkers on two or more occasions. The trending of ADAMTS13 activity illustrated that it is not steady throughout the hospitalization course. ADAMTS13 activity levels tended to improve and/or reach normal levels in patients that survived, yet ADAMTS13 activity levels worsened in most patients that died. Likewise, the VWF antigen and activity levels tended to decrease in patients that survived whereas tended to increase well above the normal range (2-3 folds) in patients that died. D-Dimer levels trended downwards in survivors, sometimes to levels less than 1 µg/ml, yet tended to increase in patients who died. Given the relationship between ADAMTS13 activity and mortality, we wanted to determine a cut-point of initial ADAMTS13 activity (within 72 hours from admission) to predict mortality. 102 patients in our cohort had an ADAMTS13 activity measurement within this timeframe. We determined that this optimal cut-point of initial ADAMTS13 activity was 43% using Youden’s J statistic. Only 30% of patients who had an ADAMTS13 activity level of less than 43% on admission survived, yet 60% of patients survived who had an ADAMTS13 activity level of greater than 43% on admission. Conclusions: COVID-19 may present with low ADAMTS13 activity in a subset of hospitalized patients. Presence of schistocytes/RBC fragment and elevated D-dimer levels on admission may warrant a work-up for ADAMTS13 activity and VWF antigen and activity levels. These findings indicate the need for future investigation to study the relationship between endothelial and coagulation activation and the efficacy of treatments aimed at prevention and/or amelioration of microangiopathy in COVID-19.

Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is a potentially fatal thrombotic microangiopathy caused by autoantibody-mediated severe deficiency of ADAMTS13. Standardized definitions of response, exacerbation, remission and relapse were initially proposed in 2003 and modified by the International Working Group (IWG) for TTP in 2017. These definitions, which have been widely used in clinical practice and research, are based primarily on the platelet count and are benchmarked against the timing of discontinuation of therapeutic plasma exchange (TPE). They do not incorporate ADAMTS13 activity or the temporizing effects of caplacizumab, a novel anti-von Willebrand factor (VWF) nanobody, on the platelet count. In light of these limitations, the IWG aimed to develop revised consensus outcome definitions that incorporate ADAMTS13 activity and the effects of anti-VWF therapy using an estimate-talk-estimate approach. The updated definitions distinguish clinical remission and clinical relapse (defined primarily by platelet count) from ADAMTS13 remission and ADAMTS13 relapse (defined by ADAMTS13 activity). The revised definitions of exacerbation and remission are benchmarked against not only the timing of discontinuation of TPE, but also of anti-VWF therapy. Retrospective validation of the revised definitions is described, though they remain to be prospectively validated. Clinical implications of the updated outcome definitions are also discussed and an example of their application to clinical practice is provided in order to highlight their clinical relevance.

Preeclampsia is a multifactorial vascular disease unique to human pregnancy. While genetic and antiangiogenic factors are important contributors to preeclampsia susceptibility, recent studies have shown that dysregulation and/or over-activation of the complement system has an integral role in dis-ease etiology. Furthermore, the role of the coagulation cascade may be underappreciated in the develop-ment of the disease. Traditionally, for research purposes, the pool of preeclampsia cases has been divided into non-severe and severe disease depending on the onset and severity of the symptoms. However, of particular interest are a small but important minority of cases that present with symptoms likening to those of hemolysis, elevated liver enzymes and low platelets syndrome, atypical hemolytic uremic syn-drome, or thrombotic thrombocytopenic purpura, all thrombotic microangiopathy (TMA) diseases, with the hallmark mechanisms of endothelial dysfunction and aberrant activation of complement and coagu-lation cascades. We therefore propose a third class, severe TMA-like preeclampsia to be included in the categorization of preeclampsia patients. Identifying these patients would target research, diagnostic dif-ferentiation, and novel treatment options to the subclass of patients with life-threatening disease that are most likely to benefit from next-generation drug development. (c) 2021 The Authors. Published by Elsevier Inc. on behalf of American Society for Histocompatibility and Immunogenetics. This is an open access article under the CC BY-NC-ND license (http://creativecommons. org/licenses/by-nc-nd/4.0/).

Background Thrombotic thrombocytopenic purpura (TTP) is a rare but potentially fatal disorder caused by ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) deficiency. Prompt identification/exclusion of TTP can thus be facilitated by rapid ADAMTS13 testing. The most commonly utilized (enzyme-linked immunosorbent assay [ELISA]-based) assay takes several hours to perform and so does not generally permit rapid testing. Objectives To evaluate the utility of a new automated test for ADAMTS13 activity, the HemosIL AcuStar ADAMTS13 Activity assay, based on chemiluminescence and able to be performed on an ACL AcuStar instrument within 33 minutes. Patients/methods This multicenter (n = 8) assessment included testing of more than 700 test samples, with similar numbers of prospective (n = 348) and retrospective (n = 385) samples. The main comparator was the Technozym ADAMTS13 Activity ELISA. We also assessed comparative performance for detection of ADAMTS13 inhibitors using a Bethesda assay. Results Overall, the chemiluminescent assay yielded similar results to the comparator ELISA, albeit with slight negative bias. ADAMTS13 inhibitor detection was also comparable, albeit with slight positive bias with the AcuStar assay. Assay precision was similar with both assays, and we also verified assay normal reference ranges. Conclusions The HemosIL AcuStar ADAMTS13 Activity assay provided results rapidly, which were largely comparable with the Technozym ADAMTS13 Activity ELISA assay, albeit lower on average. Conversely, inhibitor levels tended to be identified at a higher level on average. Thus, the HemosIL AcuStar ADAMTS13 Activity assay provides a fast and accurate means to quantitate plasma levels of ADAMTS13 for TTP/ADAMTS13 identification/exclusion, and potentially also for other applications.

In autoantibody-mediated autoimmune diseases, autoantibody profiling allows patients to be stratified and links autoantibodies with disease severity and outcome. However, in immune-mediated thrombotic thrombocytopenic purpura (iTTP) patients, stratification according to antibody profiles and their clinical relevance has not been fully explored. We aimed to develop a new type of autoantibody profiling assay for iTTP based on the use of anti-idiotypic antibodies. Anti-idiotypic antibodies against 3 anti-spacer autoantibodies were generated in mice and were used to capture the respective anti-spacer idiotopes from 151 acute iTTP plasma samples. We next deciphered these anti-spacer idiotope profiles in iTTP patients and investigated whether these limited idiotope profiles could be linked with disease severity. We developed 3 anti-idiotypic antibodies that recognized particular idiotopes in the anti-spacer autoantibodies II-1, TTP73 or I-9, that are involved in ADAMTS13 binding; 35%, 24% and 42% of patients were positive for antibodies with the II-1, TTP73 and I-9 idiotopes, respectively. Stratifying patients according to the corresponding 8 anti-spacer idiotope profiles provided a new insight into the anti-spacer II-1, TTP73 and I-9 idiotope profiles in these patients. Finally, these limited idiotope profiles showed no association with disease severity. We successfully developed 3 anti-idiotypic antibodies that allowed us to determine the profiles of the anti-spacer II-1, TTP73 and I-9 idiotopes in iTTP patients. Increasing the number of patients and/or future development of additional anti-idiotypic antibodies against other anti-ADAMTS13 autoantibodies might allow idiotope profiles of clinical, prognostic value to be identified. ispartof: HAEMATOLOGICA vol:104 issue:6 pages:1268-1276 ispartof: location:Italy status: published

BACKGROUND Platelet (PLT) transfusions are probably harmful in patients with acquired idiopathic thrombotic thrombocytopenic purpura (aTTP). Introduction of a rapid assay for ADAMTS13 activity should reduce the time to definite diagnosis of aTTP, reduce the amount of inappropriately transfused PLT concentrates, and improve mortality and morbidity. STUDY DESIGN AND METHODS We selected 265 aTTP patients with severe ADAMTS13 deficiency. Of these, 91 patients were diagnosed by March 2005 (Period 1), when ADAMTS13 activity was measured by von Willebrand factor multimer assay, which took 4 to 7 days until the result was reported. An additional 174 patients were diagnosed after April 2005 (Period 2), when the activity was measured by a chromogenic enzyme-linked immunosorbent assay, which took 1 to 2 days. RESULTS We found no significant differences in 30-day survival rate between the two periods. Overall, 48 patients received PLT transfusions. Mortality was slightly greater between patients with (22.9%) versus without PLT transfusion (17.7%), but not significant. In Period 1, Cox proportional hazards regression analysis showed that older age (≥60 years) and PLT transfusion administration were independent factors associated with higher risks of 30-day mortality. In contrast, in Period 2, lower Rose-Eldor TTP severity score and use of plasma exchange and corticosteroid therapy were independent factors associated with higher survival rates while nonadministration of PLT transfusions was not. CONCLUSION Our results indicate that PLT transfusions are harmful for aTTP patients when the definite diagnosis of severe ADAMTS13 deficiency is delayed. If it can be done as soon as possible, PLT transfusions for severe bleeding or surgical interventions might be allowed with subsequent plasmapheresis.

Background: Acquired thrombotic thrombocytopenic purpura (aTTP) is a rare and life-threatening hematologic disorder. The decision to start plasma exchange is challenging in clinical practice, due to aTTP rarity, and the extensive differential diagnosis with other thrombotic microangiopathies (TMA). Although the ADAMTS13 activity measurement is essential to aTTP diagnosis, a rapid quantification is unavailable in most centers, being necessary to develop clinical prediction models to evaluate severe enzymatic deficiency. The first model developed was Bentley score, followed by French score and more recently PLASMIC score. Studies comparing these 3 methods are scarce. The criteria of published scoring models are summarized in Table1 Aim: To compare and evaluate the discriminative power of the Bentley, French and PLASMIC scores in predicting severe ADAMTS13 deficiency (≤10%) in our group of patients (pts). Methods: We performed a retrospective analysis of pts with ADAMTS13 activity tested between 2008 and 2019, in a single center. Pts were divided in two groups: ADAMTS13 activity ≤10% (ADAMTS13≤10%) and >10% (ADAMTS13>10%) and then stratified according to the 3 scores. We evaluate sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) to predict low ADAMTS13 activity. Diagnostic accuracy was tested using the area under the ROC curve. A P-value of Results: ADAMTS13 activity was evaluated in 119 pts with suspected aTTP. There was a female predominance (60.5%; n=72) and the mean age was 54±20 years. Thirty-one pts had ADAMTS13≤10% and 27 (87.1%) of them had been diagnosed with aTTP, two were inherited thrombotic thrombocytopenic purpura and the other two were sepsis associated TMA. Comparing the groups ADAMTS13≤10% and ADAMTS13>10%, pts in the first were younger (46±18 vs 57±21 years; p=0.008), had lower platelet count (23.04±27.1 vs 47.79±37.6x109/L; p PLASMIC score was calculated in all pts. Due to missing data, Bentley score was only applied in 44.5% (n=53) and French score in 54.6% (n= 65) pts. Using a high-risk PLASMIC score as the predictor, the sensitivity was 80.6%, specificity 78.4%, PPV 56.8% and NPV 92.0%. The C-statistics for high PLASMIC score cut-offs (>5 points) was 0.80 (95% confidence interval [CI] 0.70-0.89) (fig.1). Applying high-risk Bentley score vs low-to-intermediate-risk score, the sensitivity was 44.4%, specificity 94.3%, PPV 80.0% and NPV 76.7%. The C-statistics was 0.69 (95% CI 0.53-0.86) using the high Bentley score cut-offs (fig.2). The French score had higher sensitivity (83.3%), but lower specificity (36.2%), with 33.3% of PPV and 85.0% of NPV. Using the high French score cut-offs, the C-statistics was 0.60 (95% CI 0.45-0.75) (fig.3). There were not statistically significant differences between PLASMIC and Bentley scores in the ability to predict low ADAMTS13 activity, and both performed better than French score (p Conclusion: In our cohort, the PLASMIC score showed to be the most balanced and efficient clinical prediction score, with high sensitivity and specificity. Bentley score was also a good predictor of ADAMTS13 activity, but had lower sensitivity and less applicability; French score was comparatively inferior. Pts with low PLASMIC score are highly unlikely to have ADAMTS13 deficiency. PLASMIC score is easy to calculate and readily usable in most emergency settings while the French and Bentley scores require additional laboratory data, which is not always accessible. These results support the previously published data, showing PLASMIC score as a helpful complementary tool in clinical practice recognizing high-risk pts when ADAMTS13 activity measurement is not available. Disclosures No relevant conflicts of interest to declare.

ADAMTS13 (A Disintegrin and Metalloprotease with ThromboSpondin type 1 motifs) activity is a key tool in differential diagnosis of thrombotic microangiopathies (TMAs). Due to the lack of availability of ADAMTS13 testing, PLASMIC/PLASIC scores have been suggested to predict ADAMTS13 deficiency. The importance of differentiating TTP from other complement-mediated TMAs is highlighted by the need to urgently start plasma exchange and utility of treatments such as caplacizumab or eculuzimab. Therefore, we aimed to evaluate ADAMTS13 activity, PLASMIC/PLASIC scores, and complement testing in guiding management of a real-world TMA cohort. We enrolled consecutive TMA patients with samples referred to our Center (01/2018–2020). If ADAMTS13 ​> ​10%, soluble C5b-9 was measured. Among 80 TMA patients, ADAMTS13 activity was ≤10% in 50 patients, while 28 had a relapsing disease. PLASMIC/PLASIC were excellent predictors of ADAMTS13 deficiency, especially in patients without secondary causes. Soluble C5b-9 levels were elevated (median 525 ​ng/ml, range 313–913 ​ng/ml) in 7 patients without secondary causes and ADAMTS13 ​> ​10% (hemolytic uremic syndrome/HUS). Two were shiga-toxin associated; while 5 atypical HUS. Only 1/5 patients received eculizumab and achieved TMA resolution implemented by guidance based on soluble C5b-9 levels. In transplant-associated TMA, 8/16 patients not responding to first-line treatment received eculizumab due to elevated C5b-9 levels (median 353 ​ng/ml, range 281–1252 ​ng/ml) and achieved TMA resolution. In conclusion, our real-world data confirm that ADAMTS13, complement testing, and PLASMIC/PLASIC are valuable tools in diagnosis and management of TMAs, but also highlight the unmet need of using available markers and treatments in clinical practice.

von Willebrand factor (VWF) is synthesised in vascular endothelial cells and released into the plasma as unusually large VWF multimers (UL-VWFMs). Sinusoidal endothelial cells are a major target of ischaemia-reperfusion injury due to liver surgery. This study aimed to clarify the effect of hepatectomy on UL-VWFMs.Thirty-five patients who underwent hepatectomy were eligible for the study. Plasma ADAMTS13 activity and VWF antigen levels were measured by enzyme-linked immunosorbent assay and multimer analysis of plasma VWF was performed according to Ruggeri and Zimmerman's method. For analyses, patients were categorised according to UL-VWFM positivity after hepatectomy.Plasma ADAMTS13 activity significantly decreased from 61.0% (27.7%-126.2%) before operation to 37.4% (20.2%-71.4%) on postoperative day 7 (p 0.001). Plasma VWF antigen levels significantly increased from 172.1% (80.5%-412.8%) before operation to 361.0% (154.7%-745.8%) on postoperative day 2, which remained high until postoperative day 7 (p 0.001). Seven patients remained UL-VWFMs-negative and 22 patients became UL-VWFMs-positive after operation. Pringle's maneuver duration was significantly longer and blood loss volume was significantly higher in the UL-VWFMs-positive group (p = 0.001 and p = 0.003, respectively). By multivariable analysis, Pringle's maneuver duration [odds ratio 1.049, 95% confidence interval (CI) 1.001-1.098; p = 0.043] was significantly associated with increased UL-VWFMs level after hepatectomy. UL-VWFMs index was significantly correlated with Pringle's maneuver duration (r = 0.444, p = 0.017).Plasma UL-VWFMs levels increased after hepatectomy due to ischaemia-reperfusion injury with Pringle's maneuver.

The PLASMIC score for the prediction of a likelihood of a severe ADAMTS13 deficiency represents a valid pre-test diagnostic tool to identify patients with thrombotic thrombocytopenic purpura.

Understanding the autoimmune etiology of acquired thrombotic thrombocytopenic purpura (TTP) has provided precision for the diagnosis and a rationale for immunosuppressive treatment. These advances have also allowed recognition of the remarkable clinical diversities of patients’ initial presentations and their long-term outcomes. These diversities are illustrated by the stories of patients from the Oklahoma TTP Registry. The initial presentation of TTP may be the discovery of unexpected severe thrombocytopenia in a patient with minimal or no symptoms. The patient may remain asymptomatic throughout treatment or may die suddenly before treatment can be started. ADAMTS13 activity may be reported as normal in a patient with characteristic clinical features of TTP, or the unexpected report of ADAMTS13 deficiency in a patient with another established disorder may lead to the discovery of TTP. ADAMTS13 activity during clinical remission is unpredictable. ADAMTS13 activity may recover and remain normal, it may remain severely deficient for many years, or it may become normal only many years after recovery. Our treatment of initial episodes and management of patients after recovery and during remission continue to change. The addition of rituximab to the treatment of acute episodes and preemptive rituximab for patients with severe ADAMTS13 deficiency during remission are reported to prevent relapse. Because TTP is uncommon, there are few data to guide these changes. Therefore our patients’ stories are profoundly influential. Their stories are the foundation of our experience, and our experience is the guide for our decisions.

Background Severe deficiency of plasma ADAMTS13 activity resulting from anti-ADAMTS13 IgG is the primary cause of immune-mediated thrombotic thrombocytopenic purpura (iTTP). Anti-ADAMTS13 IgG may bind and inhibit plasma ADAMTS13 activity and/or accelerate clearance of ADAMTS13 from the circulation. The present study aims to determine the initial and longitudinal changes of plasma ADAMTS13 activity, antigen, and anti-ADAMTS13 IgG and their relationships with clinical responses and outcomes of patients with iTTP after standard treatment. Methods Thirty-eight patients with a confirmed diagnosis of iTTP who underwent therapeutic plasma exchange (TPE) at UAB Medical Center were enrolled into the study. The study spanned from May 2015 to December 2018. An informed consent was obtained from each participant. Clinical and laboratory information was extracted from the electronic medical record and stored in the Alabama TTP Registry database. Plasma samples were collected prior to the initiation of and every 3 to 5 days after TPE until discharge. Plasma ADAMTS13 activity, antigen, and anti-ADAMTS13 IgG were determined using commercially available reagents. Mann-Whitney test, Fisher’s exact test, Spearman rank correlation, Cox proportional hazard regression, and Kaplan-Meier survival analysis were used to determine statistical significances. Results The median age of this cohort was 46.5 years old; 26 (68%) patients were female and 12 (32%) were male. Twenty-three patients (60%) were experiencing their initial episode while 15 (39%) had an exacerbation/relapse at the time of enrollment. All patients were diagnosed based on the findings of thrombocytopenia, microangiopathic hemolytic anemia, plasma ADAMTS13 activity ( Conclusion Initial and longitudinal assessment of plasma ADAMTS13 activity, antigen, inhibitor titer, and anti-ADAMTS13 IgG may be useful not only for diagnosis but also for predicting the risk of exacerbation. This may influence how we select a therapeutic modality for a better outcome. Long-term follow-up is necessary to determine whether these ADAMTS13 biomarkers at patient discharge are predictive of relapse and mortality.

ADAMTS13 is a zinc-containing metalloprotease that cleaves von Willebrand factor (VWF). Deficiency of plasma ADAMTS13 activity is accountable for a potentially fatal blood disorder thrombotic thrombocytopenic purpura (TTP). Understanding of ADAMTS13-VWF interaction is essential for developing novel treatments to this disorder.Despite the proteolytic activity of ADAMTS13 being restricted to the metalloprotease domain, the ancillary proximal C-terminal domains including the disintegrin domain, first TSP-1 repeat, cysteine-rich region, and spacer domain are all required for cleavage of VWF and its analogs. Recent studies have added to our understandings of the role of the specific regions in the disintegrin domain, the cysteine-rich domain, and the spacer domain responsible for its interaction with VWF. Additionally, regulative functions of the distal portion of ADAMTS13 including the TSP-1 2-8 repeats and the CUB domains have been proposed. Finally, fine mapping of anti-ADAMTS13 antibody epitopes have provided further insight into the essential structural elements in ADAMTS13 for VWF binding and the mechanism of autoantibody-mediated TTP.Significant progress has been made in our understandings of the structure-function relationship of ADAMTS13 in the past decade. To further investigate ADAMTS13-VWF interactions for medical applications, these interactions must be studied under physiological conditions in vivo.

Background Acquired thrombotic thrombocytopenic purpura (TTP) is an autoimmune disease in which anti-ADAMTS13 autoantibodies cause severe enzyme deficiency. ADAMTS13 deficiency causes the loss of regulation of von Willebrand factor multimeric size and platelet-tethering function, which results in the formation of disseminated microvascular platelet microthrombi. Precisely how anti-ADAMTS13 autoantibodies, or antibody subsets, cause ADAMTS13 deficiency (ADAMTS13 activity generally, Highlights • Anti-spacer domain autoantibodies are the major inhibitory antibodies in acquired TTP. • Depletion of ADAMTS13 antigen (rather than enzyme inhibition) is the prevailing pathogenic mechanism in acquired TTP.

Objective Idiopathic thrombotic thrombocytopenic purpura (TTP) is a life-threatening disorder mediated by autoantibodies directed against ADAMTS13. This provides a rationale for the use of rituximab in this disorder. We report our experience and the outcome of 10 cases of TTP (9 refractory and 1 relapsing) successfully treated with rituximab in combination with plasma exchange (PE) and other immunosuppressive treatments. Methods The diagnosis of TTP was based on clinical criteria and supported by severe deficiency of ADAMTS13 activity and presence of inhibitors in seven cases. Rituximab was started after a median of 18.6 sessions of PE (range: 5-35) at the dose of 375 mg/m2/week for 4-8 weeks. Results Complete remission was achieved in all patients after a median time of 14.4 days of the first dose (range: 6-30). After a median follow-up of 30 months (range: 8-78), eight patients were still in remission and two developed multiple relapses, treated again with the same therapy, and achieved complete responses; they are alive, and in complete remission after a follow-up of 12 and 16 months. Conclusion Rituximab appears to be a safe and effective therapy for refractory and relapsing TTP. However, longer follow-up is recommended to assess relapse and detect possible long-term side effects of this therapy.

ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin type 1 repeats, member 13) is responsible for the proteolysis of ultra-large von Willebrand factor (VWF) multimers into smaller multimers.[1] Thrombotic thrombocytopenic purpura (TTP) is a thrombotic microangiopathy (TMA) caused by severe ADAMTS13 deficiency (activity

Background. Deficient ADAMTS13 activity (TS13:act 50%. However, also iTTP patients in remission with a persistent ( Aim. Determine ADAMTS13 conformation in plasma of iTTP patients during acute TTP and remission when TS13:act is 50% and investigate if anti-ADAMTS13 autoAbs induce conformational changes in ADAMTS13. Methods. TS13:act was determined in 120 iTTP plasma samples from 4 different centers (Marseille, Milan, Budapest, Utrecht). Samples were categorized according to the presence of clinical symptoms (acute versusremission) and their TS13:act in remission (>50%, 10-50%, Results. Of the 120 iTTP plasma samples, 46 were obtained during the acute (clinical signs present) and 74 during the remission phase (clinical signs absent). Further subdividing remission samples showed that TS13:act was >50% in 41, 10-50% in 14 and 50%, confirming our previous results. Interestingly, ADAMTS13 was open in 93% and 89% of remission samples with TS13:act 10-50% and Conclusion. We show that ADAMTS13 is not only in the open conformation in iTTP patient plasma during the acute phase but also in remission when TS13:act is Disclosures Peyvandi: Octapharma US: Honoraria; Kedrion: Consultancy; Ablynx: Other: Member of Advisory Board, Speakers Bureau; Grifols: Speakers Bureau; Sobi: Speakers Bureau; Shire: Speakers Bureau; Novo Nordisk: Speakers Bureau; Octapharma US: Honoraria; Octapharma US: Honoraria; Novo Nordisk: Speakers Bureau; Kedrion: Consultancy; Roche: Speakers Bureau; Novo Nordisk: Speakers Bureau; Ablynx: Other: Member of Advisory Board, Speakers Bureau; Ablynx: Other: Member of Advisory Board, Speakers Bureau; Shire: Speakers Bureau; Sobi: Speakers Bureau; Roche: Speakers Bureau; Roche: Speakers Bureau; Shire: Speakers Bureau; Ablynx: Other: Member of Advisory Board, Speakers Bureau; Octapharma US: Honoraria; Roche: Speakers Bureau; Roche: Speakers Bureau; Grifols: Speakers Bureau; Sobi: Speakers Bureau; Ablynx: Other: Member of Advisory Board, Speakers Bureau; Sobi: Speakers Bureau; Shire: Speakers Bureau; Sobi: Speakers Bureau; Novo Nordisk: Speakers Bureau; Shire: Speakers Bureau; Kedrion: Consultancy; Novo Nordisk: Speakers Bureau; Grifols: Speakers Bureau; Grifols: Speakers Bureau; Kedrion: Consultancy; Kedrion: Consultancy; Grifols: Speakers Bureau; Octapharma US: Honoraria. Coppo:Ablynx: Consultancy. Veyradier:LFB: Other: Investigator. Vanhoorelbeke:Shire: Consultancy; Ablynx: Consultancy.

In the implementation of American Society for Apheresis national guidelines, the decision for therapeutic plasma exchange may be confounded by a clinical presentation that fits both a Category I and IV designation. We report the case of a 45-year-old female who presented with concern for a Category IV disorder, gemcitabine-induced thrombotic microangiopathy, and was ultimately diagnosed with a Category I disorder, idiopathic thrombotic thrombocytopenic purpura. This case highlights the importance of ruling out idiopathic TTP by a thorough evaluation for ADAMTS13 activity and inhibitor, even when an alternate thrombotic microangiopathy diagnosis may be likely.

Background: ADAMTS13 cleaves and inactivates von Willebrand factor (VWF), which binds collagen, facilitating platelet adhesion under vascular injury. But is still uncertain how ADAMTS13 activity is regulated. Thrombin and plasmin have been shown to cleave ADAMTS13. Based on the fact that elevated levels of FXI is an independent risk factor for deep vein thrombosis and ischemic stroke, we hypothesize that FXIa inactivates ADAMTS13 leading to platelet aggregation and thrombus formation. Aim: To determine the functional role of inactivation of ADAMTS13 by FXIa. Methods and Results: Recombinant ADAMTS13 (250 nM) was incubated with FXIa (50 nM) for increasing times (0-3 hours) at 37 o C before being analyzed by western blot using an anti-ADAMTS13 antibody against the two CUB domains (C-terminal) or against the metalloproteinase (MET) domain (N-terminal). Our results show that FXIa caused the disappearance of the ADAMTS13 band (~200 kDa) and the appearance of a band at ~150 kDa when the samples were analyzed with the anti-MET antibody and a ~50 kDa band when the samples were analyzed with the anti-CUB antibody. The presence of aprotinin, which inhibits FXIa activity, blocked the degradation of ADAMTS13. Kallikrein or FXIIa were unable to cleave ADAMTS13. Using a cell surface immunoassay we observed that after incubation with FXIa, the detection of the CUB domain from ADAMTS13 was lost from endothelial cells surface. The incubation of ADAMTS13 with FXIa caused an increase in ADAMTS13 activity as measured by a fluorogenic substrate (FRETS). Conclusion: ADAMTS13 circulates in a closed conformation, which is maintained by a CUB-spacer domain binding interaction. ADAMTS13 becomes conformationally activated through interaction of its CUBs domains with VWF. Here we show that FXIa-mediated deletion of ADAMTS13-CUB domains enhances its capacity to cleave FRETS and blocks the interaction with VWF. Our results suggest that FXIa may limit ADAMTS13-mediated VWF inactivation.

Context.—Acquired thrombotic thrombocytopenic purpura (A-TTP) is a rare but significant disease requiring rapid diagnosis and treatment. The diagnosis is often difficult because of variability in the presence of specific clinical criteria. The primary etiology of A-TTP involves inhibitors directed against ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13). Literature has shown that the ADAMTS13 activity assay is sensitive and specific for identifying cases of A-TTP, and application of this test as an on-site screening method has not been fully explored. Objective.—Our objective is to determine if the ADAMTS13 activity assay can be used as a successful, on-site diagnostic modality to rapidly identify cases of A-TTP and prevent unnecessary use of prophylactic therapeutic plasma exchange. Design.—A retrospective analysis was performed including 152 patients with clinically suspected A-TTP, screened using the ADAMTS13 activity assay. Results were correlated with potential therapeutic plasma exchange treatment for all cases highly suspicious for A-TTP and evaluated for unnecessary patient morbidity and financial cost. Results.—The ADAMTS13 activity assay had an overall sensitivity and specificity of 100% and 99%, respectively. The positive predictive value was 91% and the negative predictive value was 100%. In 95% of the studies ordered, A-TTP was ruled out, leading to decreased patient morbidity and $1.7 million of potential treatment costs avoided. Conclusion.—Implementation of the fluorescence energy transfer–based ADAMTS13 activity assay as a point-of-care laboratory study decreased patient morbidity while also directing more efficient employment of therapeutic plasma exchange in cases of suspected A-TTP.