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Introduction Accurate evaluation of ADAMTS13 activity is required for the diagnosis and clinical management of thrombotic microangiopathies, and commercial kits are available for routine laboratory use. Methods Our study compares the results from Technoclone (Technoclone GmbH, Austria) activity and Inhibitor kits with specialist laboratory reference methods (FRETS and ELISA IgG) and the impact of transporting frozen samples and comparison of results. Results This multicentre study identified differences in Technoclone activity results compared to specialist testing, which could potentially impact diagnosis. A change in the commercial kit during the study period appears to have rectified the detection levels. Frozen samples provided comparable results between sites. Conclusion With close attention to normal ranges, commercial kits are suitable for use in the clinical diagnosis of thrombotic microangiopathies and frozen transportation of samples between sites is a suitable approach. However, a robust external quality control system is essential to provide an independent evaluation of changes in kit production.

Background Thrombotic thrombocytopenic purpura (TTP) is a life-threatening diagnosis requiring prompt initiation of therapeutic plasma exchange (TPE). Measurement of immature platelet (PLT) fraction (%-IPF) differentiates PLT consumption or destruction from hypoproduction. Study Design and Method Our study evaluated %-IPF changes over the course of TTP treated with TPE and as a measure of treatment efficacy. Eleven idiopathic TTP patients, two human immunodeficiency virus (HIV)-associated TTP patients, and five non-TTP patients with thrombocytopenia were enrolled into our study. All patients were treated with TPE and had ADAMTS13 activity measured. Results All idiopathic TTP patients had a significantly increased %-IPF and decreased absolute immature PLT count (A-IPC) and PLT count at presentation. An A-IPC value of less than 5 × 109/L at presentation has 84.6% sensitivity, 80% specificity, and 91.7% positive predictive value for diagnosing TTP. A concurrent steady decline in %-IPF and increased PLT counts toward normal was observed in TTP patients undergoing TPE. The A-IPC, however, showed an increase and decrease curve that was not seen in the two HIV-associated TTP patients with no response to TPE and the five non-TTP patients. More importantly, reaching an A-IPC ratio of 3 compared to baseline value during TPE can readily differentiate idiopathic TTP from the other two groups and is correlated with good clinical responses to TPE. An abrupt increase of A-IPC during TPE was also noted in a TTP patient who relapsed 3 days before PLT count decrease. A-IPC is positively correlated with ADAMTS13 activity at presentation but negatively correlated with ADAMTS13 activity during recovery. Conclusion A-IPC should be routinely analyzed for diagnosing and monitoring TTP patients.

Background Thrombotic thrombocytopenic purpura (TTP) requires immediate treatment with plasma exchange (PE) to prevent disease mortality and/or morbidity. Frequently, PE is initiated before blood sample is collected to confirm ADAMTS13 deficiency. However, the effect of PE treatments on the evaluation of ADAMTS13 is uncertain. Moreover, the pertinence of ADAMTS13 activity during PE therapy to prediction of treatment outcomes is unclear. Thus, clarification of the diagnostic and prognostic values of ADAMTS13 activity obtained during PE treatment is an unmet clinical need. Study Design and Methods A total of 212 sequential samples were obtained during the course of daily PE treatment from 19 patients with acquired TTP. ADAMTS13 activity levels were determined in these longitudinal samples for analysis. Results After the initial three daily PE procedures, the sensitivities of ADAMTS13 activity in diagnosis of TTP (

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.

Background: Acquired thrombotic thrombocytopenic purpura (aTTP) is a rare but life-threatening thrombotic microangiopathy, with an untreated mortality rate of >90%. Prompt treatment with therapeutic plasma exchange (TPE) and immunosuppression improves outcomes in patients with aTTP, but 10-20% of patients still die acutely from this disease. The aim of this analysis was to describe in more detail the characteristics and disease courses of the patients who died during the caplacizumab clinical development program. Methods: Patient narratives on all deaths occurring during the phase 2 TITAN and phase 3 HERCULES studies were extracted. Results: In the overall study periods, a total of 6 patients died, 2 patients enrolled in TITAN (Patients 1 and 2) and 4 patients enrolled in HERCULES (Patients 3-6). Five patients received placebo, while 1 (Patient 6) received caplacizumab. Demographics and baseline disease characteristics are summarized in Table 1. The patient narratives are provided below. Patient 1 (placebo) was a 57-year-old male, with a recurrent episode of aTTP. Baseline platelet count was 25 x109/L and ADAMTS13 activity Patient 2 (placebo) was a 49-year-old female, with an initial presumed aTTP episode. Baseline platelet count was 7 x109/L and baseline ADAMTS13 activity was 75%. The patient did not respond to therapy (TPE and corticosteroids), with platelet counts remaining below 35 x109/L over the whole period. On Day 10 of the study, the patient experienced a cerebral hemorrhage, for which study drug treatment was permanently discontinued. The patient was intubated and died the next day of cerebral hemorrhage. Patient 3 (placebo) was a 62-year-old female with an initial aTTP episode. Baseline platelet count was 18 x109/L and ADAMTS13 activity Patient 4 (placebo) was a 72-year-old female with an initial aTTP episode. Baseline platelet count was 21 x109/L and baseline ADAMTS13 activity was Patient 5 (placebo) was a 30-year-old female enrolled with her third aTTP episode. Baseline platelet count was 21 x109/L and ADAMTS13 activity Patient 6 (caplacizumab) was a 77-year-old female with her initial aTTP episode. Baseline platelet count was 38 x109/L and ADAMTS13 activity Conclusion: Although the use of TPE and immunosuppression reduces mortality in patients with aTTP, the disease is still associated with a substantial risk of mortality. The fact that all 5 immediate deaths occurred in the placebo arm suggests that the use of caplacizumab has the potential to reduce acute mortality in patients with aTTP. Table 1. Baseline demographics and disease characteristics. Table 1 Disclosures Cataland: Ablynx/Sanofi: Consultancy, Research Funding; Alexion: Consultancy, Research Funding. Scully:Alexion: Consultancy; Ablynx/Sanofi: Consultancy; Novartis: Consultancy; Shire/Takeda: Consultancy; Shire: Research Funding. Peyvandi:Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees; Grifols: Honoraria; Kedrion: Honoraria; Alnylam: Honoraria; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bioverativ: Membership on an entity's Board of Directors or advisory committees; Sanofi: Membership on an entity's Board of Directors or advisory committees; Octapharma: Research Funding. Knoebl:Roche: Consultancy; Shire/Takeda: Consultancy; Novo-Nordisk: Consultancy, Research Funding; CSL-Behring: Consultancy; Ablynx/Sanofi: Consultancy. Kremer Hovinga:Ablynx/Sanofi: Consultancy, Honoraria, Other: Honoraria go to employer (Insel Gruppe AG, Department of Hematology); Shire: Consultancy, Other: Honoraria go to employer (Insel Gruppe AG, Department of Hematology), Research Funding; CSL-Behring: Honoraria, Other: Honoraria go to employer (Insel Gruppe AG, Department of Hematology); Roche: Honoraria, Other: Honoraria go to employer (Insel Gruppe AG, Department of Hematology); Siemens: Honoraria, Other: Honoraria go to employer (Insel Gruppe AG, Department of Hematology). Coppo:Ablynx/Sanofi: Consultancy; Alexion: Consultancy; Shire: Consultancy. Metjian:Genentech: Consultancy, Research Funding; AblynxNV/Sanofi: Consultancy, Research Funding. De La Rubia:Takeda: Consultancy; AMGEN: Consultancy; Janssen: Consultancy; Celgene Corporation: Consultancy; AbbVie: Consultancy. Pavenski:Ablynx: Honoraria, Research Funding; Bioverativ: Research Funding; Shire: Honoraria; Octapharma: Research Funding; Alexion: Honoraria, Research Funding. De Winter:Ablynx, a Sanofi company: Employment. Callewaert:Sanofi (formerly employed by Ablynx, a Sanofi company): Employment.

Introduction: Increases in plasma von Willebrand Factor (vWF) levels, accompanied by decreases in its respective metalloprotease, ADAMTS13, have been demonstrated in diseases of microvascular injury. We hypothesized that following severe trauma, a burst of ultra-large vWF (UL-vWF) is released into the bloodstream by damaged endothelium, resulting in increased thrombogenicity due to circulating vWF multimers. We further hypothesized that traumatic injury would lead to a deficit of ADAMTS13, promoting the accumulation of UL-vWF forms and, ultimately, the increased risk of microvascular disease, such as acute kidney injury (AKI). Methods: A cohort of 37 severely injured trauma patients was analyzed for antigen levels of plasma vWF and ADAMTS13 at 0- and 24-hours after admission. Circulating vWF multimeric composition from both time points was determined by vertical agarose gel electrophoresis. Multivariate analyses were performed with data abstracted from the electronic medical records to identify further dependences. A similar analysis was also performed on plasma from a cohort of 8 patients with trauma induced AKI at 0-, 24-, and 72-hours after admission; these patients were well matched against trauma patients without AKI. Finally, we utilized a murine model of polytrauma and hemorrhage, in conjunction with qRT-PCR of ADAMTS13 in total liver RNA, to specifically address how the expression of ADAMTS13 is altered by the systemic effects of traumatic injury. Results: Circulating vWF levels were increased in severe trauma patients when compared to healthy controls at presentation (189% (110-263) vs. 95% (74-120)) and persisted through 24-hours (213% (146-257) vs. 132% (57-160)). Ultra-large vWF forms were elevated at both 0- and 24-hours when compared to pooled normal plasma ((10.0% (8.9-14.3) and 11.3% (9.1-21.2), respectively, vs 0.6%). The largest vWF forms within trauma patient plasma circulated at 33±4 dimers vs 18±1 dimer in length within pooled normal plasma. Severe trauma patient ADAMTS13 activity was decreased at 0-hours (66% (47-86) vs. 100% (98-100)) and at 24-hours (72.5% (56-87.3) vs 103% (103-103)) when compared to healthy patients. Furthermore, the proportion of circulating low molecular weight multimeric (LMWM) vWF to total circulating vWF forms was directly dependent upon ADAMTS13 activity at 24-hours (Decreased ADAMTS13 Activity: 20.4% (15.0-22.7) LMWM vWF vs Normal Activity: 25.8% (22.7-35.2) LMWM vWF). Strikingly, ADAMTS13 activity independently predicted the development of coagulopathy, correlating with presentation INR (ρ =-0.63), activated clotting time of thromboelastography (TEG) (ρ=-0.36), and TEG maximum amplitude (ρ=0.36). ADAMTS13 activity also closely correlated with injury severity (ISS) (ρ=-0.34) and blood product transfusion (ρ =-.45). The cohort of 8 trauma patients who went on to develop AKI showed a 1.54-fold (1.02-2.05) increase in plasma vWF antigen levels between 0 and 72 hours, while those who did not develop AKI showed no change in vWF levels over this time period. Furthermore, those who developed AKI demonstrated a smaller proportion of LMWM vWF in plasma than those who did not (25.4% (23.4-28.0) vs 31.2% (27.2-35.6)), suggesting the increased thrombogenicity of their circulating vWF forms. Finally, qRT-PCR of total liver RNA in 6 mice demonstrated a 2-fold decrease in ADAMTS13 RNA expression levels between the times immediately before and 24-hours after trauma. Altogether, these data indicate that both circulating ADAMTS13 and its production are deficient in the days following severe injury. Conclusions: Severe traumatic injury alters the circulating composition of ADAMTS13 and its target, vWF, shifting their equilibrium to one that promotes thrombosis. Not only is the concentration of circulating ADAMTS13 decreased following traumatic injury, but hepatic expression of the enzyme is lacking as well. In the immediate moments following injury, these mechanisms contribute to life-saving hemostasis; however, as these changes extend into the following days, the early hemostatic benefit quickly shifts to burden that may exacerbate microvascular disease. Disclosures Ragni: Bioverativ/Sanofi: Consultancy, Research Funding; Sangamo: Research Funding; Shire/Takeda: Consultancy, Other: Study drug; Alnylam/Sanofi: Consultancy, Research Funding; Bayer: Consultancy; Spark Therapeutics: Consultancy, Research Funding; ICER: Consultancy; OPKO: Research Funding; Biomarin: Consultancy, Research Funding. Rollins-Raval:Bayer, Inc: Membership on an entity's Board of Directors or advisory committees. Raval:Sanofi: Membership on an entity's Board of Directors or advisory committees; Bayer, Inc: Research Funding. Neal:Janssen Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees; CSL Behring: Membership on an entity's Board of Directors or advisory committees.

Background: It is commonly accepted that severely deficient ADAMTS13 activity in remission increases the risk for relapse, but relapse in severely deficient ADAMTS13 activity in patients with immune-mediated thrombotic thrombocytopenic purpura (iTTP) is not uniform. Mouse models and published studies have suggested that a "second hit" is required in addition to severely deficient ADAMTS13 activity to lead to clinical relapse. Our initial published experience led us to preliminarily conclude that pregnancy could serve as the second hit in addition to severely deficient ADAMTS13 activity and lead to relapse. The aim of this study was to evaluate the risk of relapse and outcomes of pregnant patients with a diagnosis of iTTP. Methods: Since the initiation of the Ohio State University TTP Research Program in 2003, patients were consented at enrollment and followed longitudinally in our IRB approved iTTP registry, usually every three to six months. During pregnancy, patients were seen and CBC, LDH and ADAMTS13 activity were obtained monthly. Due to prior reports of iTTP relapses during pregnancy, it is our practice to offer prophylaxis with cyclosporine to pregnant patients with a diagnosis of iTTP and severely deficient ADAMTS13 activity. The clinical diagnosis of iTTP (defined as thrombocytopenia, microangiopathic hemolytic anemia, without an alternative explanation was confirmed by severely deficient ADAMTS13 activity ( Results: During the study time, we have followed 11 pregnancies from eight patients with iTTP. Two pregnancies occurred at the time of their initial diagnosis, and nine pregnancies occurred during follow up. Two patients were black, nine were white. Median age was 26 ( range 20-36). Of the nine pregnancies in patients with a previous diagnosis of iTTP, three resulted in relapses, two in the same patient; one at 23 weeks that resulted in fetal demise, and the next one occurred one week after delivery at 36 weeks. The other patient relapsed at 35 weeks and the baby was delivered early at 36 weeks. All relapses were preceded by a documented ADAMTS13 Conclusions: Pregnancy in patients with a diagnosis of iTTP is a risk factor for iTTP relapse. To our knowledge, this is the first report of the relationship between ADAMTS13 and the risk of relapse during pregnancy. Our results demonstrate that severely deficient ADATMS13 activity uniformly leads to relapse in pregnancy. It also highlights the clinical relevance of monitoring ADAMTS13 activity closely in patients with a history of iTTP that become pregnant. Figure 1 Disclosures Masias: Rigel Pharmaceuticals: Consultancy. Cataland:Alexion: Consultancy, Research Funding; Ablynx/Sanofi: Consultancy, Research Funding. OffLabel Disclosure: the use of cyclosporine for prevention of TTP relapses

SummaryCollagen-binding activity (CBA) and FRETS-VWF73 assays are widely adopted methods for the measurement of the plasmatic activity of ADAMTS13, the von Willebrand factor (VWF) cleaving-protease. Accurately assessing the severe deficiency of ADAMTS13 is important in the management of thrombotic thrombocytopenic purpura (TTP). However, non-concordant results between the two assays have been reported in a small but relevant percentage of TTP cases. We investigated whether CBA or FRETS-VWF73 assay reflects ADAMTS13 proteolytic activity in acquired TTP patients with non-concordant measurements. Twenty plasma samples with non-concordant ADAMTS13 activity results

Thrombocytopenia, in the setting of microangiopathic hemolytic anemia and thrombotic events, is characteristic of both thrombotic thrombocytopenic purpura and primary antiphospholipid syndrome. Clinically, it is difficult to distinguish between these two syndromes. We present a 41-year-old woman with chronic, relapsing thrombotic thrombocytopenic purpura in the presence of antiphospholipid antibodies. She had clinical manifestations of antiphospholipid syndrome without meeting laboratory criteria of the Sydney classification system. In the literature, there have only been nine cases of thrombotic thrombocytopenic purpura associated with primary antiphospholipid syndrome. Seven of the nine cases suffered from one or multiple strokes, a common feature in antiphospholipid syndrome, but an uncommon finding in thrombotic thrombocytopenic purpura. We introduce the possibility of an association between thrombotic thrombocytopenic purpura and the presence of antiphospholipid antibodies. Systematic testing of ADAMTS13 activity and anti-ADAMTS13 antibodies in patients who present with neurological symptoms and thrombocytopenia, in the presence of antiphospholipid antibodies, may help with the diagnosis of the rare thrombotic thrombocytopenic purpura-antiphospholipid syndrome combination.

To the editor: Acute episodes of acquired autoimmune thrombotic thrombocytopenic purpura (TTP) are associated with severe ADAMTS13 deficiency, commonly defined as

We report a case of a 64-year-old man who, 44 days after starting treatment with prasugrel, presented with severe thrombocytopenia, anaemia, renal failure, and severe ADAMTS13 activity deficiency, along with a high titer of autoantibodies to this protease. LEARNING POINTS Drug-induced TTP is a rare condition and difficult to diagnose. Decreased activity of ADAMTS13, unusual in drug-induced TTP, was present in this case.

We report the case of a 68-year-old woman with acute thrombotic thrombocytopenic purpura (TTP) that developed after pneumococcal vaccination. She was found in a confusional state with high fever 15 days after vaccination. Laboratory data showed hemolytic anemia and thrombocytopenia, and blood smear showed fragmented erythrocytes. TTP was diagnosed based on the clinical presentation, and was subsequently confirmed by the absence of ADAMTS13 activity and the presence of inhibitor against ADAMTS13 in serum. She was successfully treated using plasma exchange and corticosteroids, and no recurrence has been identified. This appears to represent the first report of TTP following pneumococcal vaccination.

The present study examined von Willebrand factor (vWF) levels and ADAMTS13 activity in pregnant and severe preeclamptic women in order to shed light on the prothrombotic state in severe preeclampsia. Thirty healthy women of childbearing age, 22 second trimester pregnant women, 30 third trimester pregnant women and 10 severe preeclamptic patients were recruited in this study. ADAMTS13 activity was determined by the FRETS-vWF73 assay and vWF antigen (vWF:Ag) levels by an enzyme-linked immunosorbent assay. The results showed that there were statistically significant differences in plasma vWF antigen levels between the severe preeclamptic and third trimester pregnant women, between third and second trimester pregnant women (P0.05). The third trimester pregnant women had significantly lower plasma ADAMTS13 activity than second trimester pregnant women (P0.05). Nevertheless, no significant differences in plasma ADAMTS13 activity were found between severe preeclamptic patients and the third trimester pregnant women (P0.05). In conclusion, plasma ADAMTS13 activity is normal in severe preeclampsia despite the increased vWF:Ag levels. Prothrombotic state is involved in the pathogenesis of severe preeclampsia, as a result of endothelial injury.

ADAMTS13は，止血因子であるフォンビレブランド因子（VWF）のA2ドメイン内のTyr1605-Met1606間のペプチド結合を特異的に切断する酵素である．この切断により新たに生じるペプチドのC末端Tyr1605を特異的に認識するモノクローナル抗体を用いて，基質の切断生成物をELISA法で直接測定する原理に基づいたADAMTS13活性測定法のキット化を行い，そのキットの基本的な性能を評価した． 本キットの最小検出感度は，健常人のADAMTS13活性100％に対して，0.4％と高感度であった．また，調製したプレート内のウエル間の均一性（変動係数（CV）=3.3％）は良好で，濃度の違う検体での同時再現性（CV=1.1～4.7％）及び日差再現性（CV=2.6～7.5％）も良好であった．希釈試験では，原点に回帰する良好な直線性が得られた．またヘモグロビンやビリルビン等の共存物質の影響は，検討した濃度範囲では認められなかった．反応はEDTAで完全に阻害された． 臨床検体及び健常人検体を本キットで測定したときのADAMTS13活性は，健常人プール血漿100％に対し先天性のADAMTS13活性欠損症であるUpshaw-Schulman症候群（USS）で0.5％以下～2.7％，USS保因者群で7.7～85.3％，血栓性血小板減少性紫斑病（TTP）群で0.5％以下～58.1％，健常人で54.7～134.4％と測定され，TTPの診断に必要な判別能を有しており，SDS-agaroseゲル電気泳動法との相関は相関係数（r）=0.931と良好であった．本キットは優れた性能と操作性を有していることから，TTPの診断や血小板輸血時の適否判断などにおいて有用であると考えられた．

Background: ADAMTS13 is the enzyme responsible for cleaving ultra-large von Willebrand factor (vFW) multimers. Commercial kits have been recently developed that use a fluorescence resonance energy transfer (FRET) methodology to measure ADAMTS13 activity. Methods: In this study, we compared the results from 2 recently released commercial kits (GTI and Technoclone) with results obtained from a reference laboratory also using FRET technology to assay samples from patients referred for a possible diagnosis of thrombotic thrombocytopenic purpura (TTP). Results: A total of 29 samples were assayed and compared. Six samples had less than 5% of normal ADAMTS13 activity identified by the reference laboratory. The GTI kit identified only 4 of these 6 samples, while the Technoclone kit identified all 6. Conclusion: The results of this study demonstrate that commercial ADAMTS13 activity assays currently available are clinically useful in diagnosing TTP.

We aimed to evaluate the ADAMTS13 activity weekly after the hematopoietic stem cell transplantation and its relationship with clinical outcome. We studied 30 patients undergoing allogeneic hematopoietic stem cell transplantation with different conditioning regimens and 15 healthy controls. Plasmas were collected from patients 10 days before transplantation, the day of transplantation and 7th, 14th, 21st and 28th days after transplantation. Patients were followed for median period of 13 months (6-24 months). Patient plasmas were further collected when graft versus host disease (GVHD) developed. Enzyme activities of patients did not show a significant change through weeks [87% (39-145), 82% (16-110), 80% (36-134), 80% (36-134), 86% (47-127), 89% (11-127) and 90% (10-127)]. None of our patients had enzyme activity lower than 5% and had thrombotic microangiopathy, thromboembolism or hepatic veno-occlusive disease. Enzyme activity on the day of acute GVHD was not significantly different from the pretransplantation period (73 +/- 32 versus 87 +/- 20%, P = 0.231), but significantly lower than healthy controls (73 +/- 32 versus 97 +/- 16%, P = 0.02). Moreover, by the 28th day after transplantation, patients with acute GVHD had lower enzyme activity than the patients without acute GVHD (62 +/- 36 versus 95 +/- 22%, P = 0.009). ADAMTS13 activity was lower in samples taken from patients with chronic GVHD compared with baseline level (67 +/- 13 versus 91 +/- 30%, P = 0.15) and healthy controls (67 +/- 13 versus 97 +/- 16%, P = 0002). According to our data, transplantation does not have significant effect on ADAMTS13 activity. Acute or chronic GVHD causes a slight decrease of the enzyme that may indicate the possible cytokine effect.

SummaryDecreased plasma ADAMTS13 activity (ADAMTS13:AC) results in the accumulation of unusually large von Willebrand factor multimer (UL-VWFM) and the formation of platelet thrombi. It remains controversial whether or not plasma ADAMTS13:AC decreases in patients with liver cirrhosis (LC), and its relationship to clinical features has not been fully investigated. We measured ADAMTS13:AC and its related parameters in plasma in 33 patients with chronic hepatitis (CH) and in 109 patients with LC. ADAMTS13:AC decreased with increasing severity of liver disease (controls means 100%, CH 87%, Child A-LC 79%, Child B-LC 63%, and Child C-LC 31%), and showed severe deficiency (

Differential diagnosis between thrombotic thrombocytopenic purpura (TTP) and other thrombotic microangiopathies (TMA) is usually difficult because of frequently overlapping clinical presentations. Severely depressed ADAMTS13 activity (

Background The von Willebrand factor (VWF)-cleaving protease, ADAMTS13, is often deficient in cases of thrombotic thrombocytopenic purpura (TTP). The primary treatment of TTP is therapeutic plasma exchange (TPE) utilizing a variety of plasma products that help restore ADAMTS13 activity. However, multiple replacement products are available to choose from. Thawed plasma products have a variable refrigerated shelf life depending on the product type; stability of ADAMTS13 in thawed products stored at 1 to 6 degrees C has not been determined. Study design and methods ADAMTS13 activity was measured in three types of plasma products and cryoprecipitate. Fresh-frozen plasma (FFP) aliquots and cryoprecipitate-poor plasma (CPP) products were produced from 10 whole-blood (WB) donations. Twenty-four-hour plasma products were manufactured from 10 additional WB donations. ADAMTS13 activity in these products at time of thaw and after 5 days of storage at 1 to 6 degrees C was measured with a modified version of the FRETS-VWF73 fluorogenic assay. ADAMTS13 activity at time of thaw was measured in 10 units of cryoprecipitate and five related CPP products. Results ADAMTS13 is present in similar amounts in FFP, CPP, and 24-hour plasma products. Storage at 1 to 6 degrees C for up to 5 days did not significantly diminish ADAMTS13 activity. The concentration of ADAMTS13 in cryoprecipitate was significantly higher than that observed in plasma products. Conclusion FFP, CPP, and 24-hour plasma products should be equally effective for ADAMTS13 restoration through TPE and should remain so for the duration of the shelf life of the thawed products.

The first approach to a patient with thrombotic microangiopathy (TMA) involves differentiating thrombotic thrombocytopenic purpura (TTP) from hemolytic uremic syndrome (HUS), since both pathogenesis and treatment differ. Case-by-case decision making based on all the clinical, laboratory and response-to-therapy criteria can result in an accurate diagnosis, leading to the most appropriate therapy and a better chance of improving clinical outcome while preserving organ function. We report the case of a 21-year-old female admitted for TMA characterized by severe renal involvement and no neurological symptoms. Clinical onset occurred after a three-day long episode of diarrhea. First analysis showed no evidence of shiga toxin-producing E. Coli (STEC) and revealed severely deficient ADAMTS13 activity, which is common in TTP. After an initial response to steroids and plasma exchange therapy (PEX), the patient became PEX-dependent. A complete remission and PEX-independence was achieved by a B cell depletion therapy with Rituximab. Results of the subsequent genetic analysis showed a new heterozygous variant p.Arg448Leu, as an isolated mutation, in the complement factor I gene.

BACKGROUND Plasma stored refrigerated for up to 5 days after thawing is common practice in many US hospitals. Therefore, clotting factor activities in fresh-frozen plasma (FFP), plasma frozen within 24 hours (PF24), and solvent/detergent-treated plasma (SDP), thawed and stored at 1 to 6°C for up to 5 days, were investigated. STUDY DESIGN AND METHODS Five A, B, O, and AB units of FFP, PF24, and SDP were thawed and maintained for 5 days at 1 to 6°C. The activity of factor (F)V, FVII, FVIII, protein S (PS), and ADAMTS13 was determined in each unit at baseline and every 24 hours thereafter for 5 days. RESULTS After thaw, mean values of the variables tested were within the normal range in all three plasma products although, in SDP, FVIII activity was significantly lower (p = 0.0039). After 5 days of storage all factors significantly declined except for ADAMTS13 activity, which was stable. Mean FVIII and ADAMTS13 activity was comparable in all three plasma products and within the normal range, mean FV activity was significantly lower in FFP and PF24 (p

The complex relation between thrombotic thrombocytopenic purpura (TTP) and pregnancy is concisely reviewed. Pregnancy is a very strong trigger for acute disease manifestation in patients with hereditary TTP caused by double heterozygous or homozygous mutations of ADAMTS13 (ADisintegrin And Metalloprotease with ThromboSpondin type 1 domains, no. 13). In several affected women disease onset during their first pregnancy leads to the diagnosis of hereditary TTP. Without plasma treatment mother and especially fetus are at high risk of dying. The relapse risk during a next pregnancy is almost 100% but regular plasma transfusion starting in early pregnancy will prevent acute TTP flare-up and may result in successful pregnancy outcome. Pregnancy may also constitute a mild risk factor for the onset of acute acquired TTP caused by autoantibody-mediated severe ADAMTS13 deficiency. Women having survived acute acquired TTP may not be at very high risk of TTP relapse during an ensuing next pregnancy but seem to have an elevated risk of preeclampsia. Monitoring of ADAMTS13 activity and inhibitor titre during pregnancy may help to guide management and to avoid disease recurrence. Finally, TTP needs to be distinguished from the much more frequent hypertensive pregnancy complications, preeclampsia and especially HELLP (Hemolysis, Elevated Liver Enzymes, Low Platelet count) syndrome.

Background Thrombotic microangiopathy (TMA) with non-deficient ADAMTS-13 (a disintegrin-like and metalloprotease with thrombospondin type 1 motif 13) outcome is unknown hence the survival analysis correlating with ADAMTS-13 activity is conducted in Malaysia. Methods This was a retrospective epidemiological study involving all cases of TMA from 2012–2016. Results We evaluated 243 patients with a median age of 34.2 years; 57.6% were female. Majority of the patients were Malay (62.5%), followed by Chinese (23.5%) and Indian (8.6%). The proportion of patients with thrombotic thrombocytopenic purpura (TTP) was 20.9%, 72.2% of which were acquired while 27.8% were congenital. Patients with ADAMTS-13 activity ≥5% had a four-fold higher odds of mortality compared to those with ADAMTS-13 activity

During the past 17 years, thrombotic thrombocytopenic purpura (TTP) has become defined by a severe deficiency of ADAMTS13.1 However this definition is not equivalent to a diagnosis of TTP. ADAMTS13 measurements have become common in our evaluation and management of patients with suspected TTP, but there are still uncertainties about the interpretation of these measurements. To address these uncertainties, we need to consider three questions. Addressing these questions is something that clinicians do whenever seeing a patient for whom the question is, “Does she have TTP?”

We report a child with thrombotic thrombocytopenic purpura (TTP) secondary to systemic lupus erythematosus. The diagnosis was confirmed by low ADAMTS13 activity (5%) along with the presence of a low titer inhibitor. Her clinical course was complicated by systemic lupus erythematosus, immunosuppressant therapy, and septic shock. She responded to plasma exchange and ADAMTS13 activity levels recovered. This case illustrates the heterogeneity of TTP and the difficulty of making a diagnosis of TTP. ADAMTS13 activity assay can be useful in the differential diagnosis of diseases with clinical features of thrombotic microangiopathy in pediatric patients. However, treatment needs to be decided carefully case-by-case.

We report a case of severe vitamin B-12 deficiency in a child who had a clinical presentation of hemolysis and thrombocytopenia that suggested the diagnosis of thrombotic thrombocytopenic purpura (TTP) and was associated with decreased ADAMTS13 activity. In this report, we review vitamin B-12 deficiency in children, the relationship between ADAMTS13 activity and TTP and discuss other conditions associated with decreased ADAMTS13 activity.

In this issue of Blood , [de Vries et al][1] report the contribution of genetic variants to plasma ADAMTS13 (disintegrin and metalloproteinase with thrombospondin motifs 13) activity with a hypothesis-free genome-wide association (GWA) approach using the Rotterdam Study, a large population-based

Comparison of FRETS-VWF73 to full-length VWF as a substrate for ADAMTS13 activity measurement in human plasma samples

A 68-year-old woman was admitted to the regional hospital because of hemolytic anemia, thrombocytopenia, and neurological abnormalities including unconsciousness. One week before admission, she suffered from diarrhea and subsequently passed out and hit her face on the ground. She was suspected of having TTP and was transferred to our hospital. We performed the assays of ADAMTS13 activity and anti-ADAMTS13 antibody titers, and confirmed the diagnosis of acquired idiopathic TTP with total deficiency of ADAMTS13 activity with its inhibitor. She was initially treated with plasma exchange combined with corticosteroids, however, we were forced to substitute plasma exchange with fresh frozen plasma infusion due to procedure-associated complications. The infusion of fresh frozen plasma was known as less effective and more likely to boost inhibitor titers compared to plasma exchange. In this circumstance, we could successfully switch the plasma therapy under close monitoring of ADAMTS13 activity and anti-ADAMTS13 antibody titers which precisely revealed the disease status of TTP in our patient, and eventually she achieved complete remission with normal level of ADAMTS13 activity and no inhibitor. Our experience suggested that the measurement of ADAMTS13 activity and inhibitor titer might be valuable not only for making the diagnosis but also for guiding treatment decisions by precise evaluating of disease status in patients with the acquired form of TTP.

The clinical presentation of thrombotic thrombocytopenia purpura (TTP) and other thrombotic microangiopathies (TMAs) can often be similar. The role of a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13) in diagnosing TTP is accepted by most researchers but continues to be debated in a few studies. We report the experience of our single-centre academic institution, where ADAMTS13 is used to diagnose TTP and guide plasma exchange (PLEX). Patients presenting to our institution with thrombotic microangiopathy (60 patients) between January 2006 and December 2012 were divided into two groups based on ADAMTS13 activity and clinical history. Patients with ADAMTS13 activity10% were included in the TTP (n = 30) cohort while patients with activity11% were classified as 'other microangiopathies' (TMA, n = 30). PLEX was only initiated in patients with a high likelihood of TTP and discontinued when the baseline ADAMTS13 activity was11%. Patients with severe ADAMTS13 deficiency (TTP group) showed significant presenting differences: lower platelet counts, less renal dysfunction, higher presence of neurological abnormalities, and greater haemolysis markers as compared to non-deficient patients (TMA group). Most importantly, patients without severe ADAMTS13 deficiency were safely managed without increased mortality despite receiving no PLEX or discontinuing PLEX after a short course (upon availability of ADAMTS13 results). In conclusion, ADAMTS13 can be used to diagnose TTP and guide appropriate PLEX therapy.

Background Cryosupernatant plasma (CSP) is used in Canada for plasma exchange in thrombotic thrombocytopenic purpura. The refrigerated storage time for thawed CSP is limited in many areas to not more than 24 hours postthaw. Because large volumes of CSP are needed for plasma exchange, procedural postponement can lead to product wastage. To determine if CSP storage could be extended, we measured coagulation-related activities in CSP thawed and stored at 1 to 6°C for up to 5 days. Study Design and Methods Thirty-six CSP units were thawed, refrigerated, and sampled aseptically at 0, 24, 48, and 120 hours postthaw. Clotting factor activities (Factor [F]V, FVII, FVIII, and fibrinogen) and prothrombin time were measured using an automated coagulation analyzer, and von Willebrand factor (vWF) and ADAMTS13 activities using enzyme-linked immunosorbent assay. Results Fibrinogen, FVIII, and vWF activities were unchanged from thaw values after 120 hours of storage; ADAMTS13, FV, and FVII activities were significantly lower than at thaw, but mean reductions were only −2.6, −7.7, and −12%, respectively. Losses were proportionately greater in the first 24 hours of refrigerated storage. Conclusions Extending the refrigerated storage of CSP from 1 to 5 days had little impact on product quality. The retention of more than 97% of initial mean ADAMTS13 activity after 5 days of refrigerated storage suggests that the shelf life of thawed refrigerated CSP could be extended without meaningful losses of its likely most important ingredients. CSP postthaw storage could be aligned to that of refrigerated thawed frozen plasma, currently available for transfusion in some jurisdictions for up to 5 days postthaw.

This study aimed to assess the von Willebrand factor (VWF) antigen levels and its proteolytic enzyme ADAMTS13 activity in preeclampsia. The study includes 10 non-pregnant women, 50 normal pregnancy, and 110 preeclamptic (PE) women at the same period of pregnancy. For all studied groups plasma ADAMTS13 activities were determined with the FRETs-VWF 73 assay, while VWF antigen levels with an immunoturbometric assay. The plasma ADAMTS13 activity was significantly reduced in PE as compared with normal pregnancy and non-pregnant women (P < 0.01 for both). In contrast, plasma VWF antigen and VWF RCO were significantly elevated in PE, as compared with normal pregnancy group as well as non-pregnant women (P < 0.01 for both). In conclusion, reduction of plasma ADAMTS13 and elevation in VWF might have a role in the pathogenesis of PE.

Thrombotic thrombocytopenic purpura (TTP) is a rare, life-threatening disease characterized by acute episodes of widespread microvascular thrombosis. The discovery that the plasmatic activity of the von Willebrand factor cleaving protease, ADAMTS13, is severely deficient in patients with TTP partially clarified the pathophysiology of the disease. However, the finding of severe deficiency of ADAMTS13 alone is unable to fully explain the clinical heterogeneity of the disease. The recent development of methods that measure ADAMTS13 activity with great analytical precision offers the opportunity to define the relationships between levels of ADAMTS13 activity below 10% (herein defined as "residual ADAMTS13 activity") and the clinical manifestations of the disease. Recent studies suggest that the amount of residual activity of ADAMTS13 may be a major determinant of the clinical heterogeneity of TTP. Herein, we review the recent findings on residual ADAMTS13 activity and their implications for research and clinical practice in the field.

Introduction: Congenital thrombotic thrombocytopenic purpura (TTP) is characterized by disseminated thrombus due to the mutations of ADAMTS13, which cleaves its substrate von Willebrand factor(VWF) in shear-induced unfolding condition. Most of the congenital TTP we found is woman with pregnancy. Here, we characterize two children suspected with congenital TTP. Methods:ADAMTS13 activities were analyzed by residual collagen binding assay (R-CBA) plus FRET-VWF substrate. And the inhibitors of ADAMTS13 were analyzed by 9:1 mixture of patient and pooled normal plasma followed by R-CBA. The secretion of recombinant ADAMTS13 mutants was studied. Results: Two children, one aged four months and the other aged three years old, were diagnosed with congenital TTP because their ADAMTS13 activities were less than 5% (both FRET-VWF and R-CBA), and there are short of ADAMTS13 inhibitors. The following mutations were found: Q1385P, Y177C, C522R. In addition to the previously reported mutation of Y177C, the two novel mutations (Q1385P and C522R) failed to secrete from the HEK293 cells. Conclusion: Two children with congenital TTP were determined thanks to screening of ADAMTS13 activity and its corresponding inhibitor assays, and it seems that congenital TTP could occur in different ages although most of congenital TTP we found were women with pregnancy. Disclosures No relevant conflicts of interest to declare.

Background:Thrombotic thrombocytopenic purpura (TTP) is a rare but deadly thrombotic microangiopathy (TMA) that is caused by an acquired deficiency in the ADAMTS13 enzyme. The PLASMIC clinical scoring system was developed and validated in 2014 by the Harvard TMA Research Collaborative in order to determine the pretest probability of severe ADAMTS13 deficiency in cases of suspected TTP. We studied the role of the PLASMIC score in guiding use of the ADAMTS13 activity assay and assessed the cost effectiveness of a score-based diagnostic approach to patients with TMA compared to two strategies currently in use within our consortium. Methods:We utilized an expanded dataset from the Harvard TMA Research Collaborative consisting of all consecutive cases of TMA at three large academic medical centers for which an ADAMTS13 assay was sent between 2004-2015 (n=647). To investigate trends in ADAMTS13 testing over time, we compared the experience at two centers (A and B) with a liberal ADAMTS13 testing policy against a third center in our consortium (C) that carries a more restrictive policy requiring pre-approval by the blood transfusion service. Cost savings analysis was subsequently performed to assess the potential impact of an algorithm incorporating the PLASMIC score for clinical decision support in the workup of these patients. Results:At Sites A and B, we observed after adjusting for changes in inpatient volume that the quantity of ADAMTS13 tests increased greater than eight-fold during the study period (from 11 per 100,000 admissions in 2004 to 94 per 100,000 admissions in 2015, P Conclusions:Taken together, our results demonstrate that a significant number of patients in our consortium who are at minimal risk for TTP nevertheless undergo ADAMTS13 testing and receive expert consultation and/or TPE. An approach incorporating upfront application of the PLASMIC clinical scoring system to risk stratify patients with suspected TTP may help enhance the cost effectiveness of diagnosing and managing these cases. Figure Figure. Table Table. Disclosures No relevant conflicts of interest to declare.

SummaryADAMTS13 activity assays are sometimes useful in confirming the clinical diagnosis or to distinguish different thrombotic microangiopathies (TMA). We investigated the commonly used clinical assays for ADAMTS13 activity. 159 samples from normal subjects or acquired TMA patients were studied in collagen binding (CBA), Fret and chromogenic peptide substrate assays. Frozen aliquots of pooled normal plasma gave similar values by CBA, Fret-VWF73 peptide, Fret-VWF86 and chromogenic VWF73 ELISA (chr-VWF73). Two lyophilised commercial calibrants gave lower ADAMTS13 activity by CBA than peptide substrate assays. The addition of solid HEPES to normal plasma caused a significant fall in CBA, but not Fret-VWF73 activity and might partly explain the differences, since lyophilised plasmas are often HEPES buffered. Normal plasmas showed good agreement between CBA and Fret assays, although chr-VWF73 gave slightly higher values. In acquired TMA, there was reasonable agreement between assays for samples with