Profiling ADAMTS13 Activity in Plasma from PatientsIndicated of Thrombotic Disorders

Research output: Contribution to conferencePaperpeer-review


Background: The metalloprotease ADAMTS13 regulates platelet adhesion by cleaving highly hemostatic active von Willebrand factor (vWF), a protein released after vascular damage. Autoimmune or genetic deficiency of ADAMTS13 activity causes a rare but fatal blood clotting disorder thrombotic thrombocytopenic purpura (TTP). Clinical symptoms of TTP include anemia, fever, thrombocytopenia, neurological abnormalities, and renal insufficiency. Many thrombotic disorders also can present with symptoms like TTP; therefore, an expedited TTP diagnosis can be challenging. However, severe ADAMTS13 activity

Aim: Determine the clinical utility of our recently validated ADAMTS13 assay, Cattle-FRETS71, using plasma samples from a diverse patient population and healthy controls.

Method: We collaborated with investigators at Duke University to profile ADAMTS13 activity levels in biobanked plasma samples(n=73) of patients indicated for heparin-induced thrombocytopenia (HIT [nonheat inactivated, and heat inactivated]), platelet factor 4 (PF4) antibodies, thrombotic microangiopathy (TMA) syndromes including thrombotic thrombocytopenic purpura (TTP), immune thrombocytopenia (ITP), and healthy donor plasma samples. This was a blinded study. Plasma samples were recalcified with 6 mM CaCl2 to neutralize the metal-chelating effects of citrate. Assays were performed at pH 7.4 in 50 mM HEPES, 150 mM NaCl, 10 mM CaCl2, and 0.05% Tween-20 buffer with 2 µM Cattle-FRETS71 substrate. Data were analyzed with Prism (GraphPad).

Results: Comparing the mean activity in each group, ADAMTS13 activity was normal (>60%) in the PF4 and ITP groups with a mean of 69.4 + 22.7% (n=17) and 99.6 + 21.7% (n=10), respectively. The highest ADAMTS13 activity was in the ITP group, which mirrored the healthy donors with a mean of 89.7 + 26.3% (n=10). HIT (non-heat inactivated) and TMA samples had a mean of 56.1 + 54.9% (n=5) and 31.4 + 31.1 % (n=24), respectively. Excluding HIT (heat-inactivated, n=6) and healthy donor samples, all patient samples had a mean of 57.3 + 38.9 % ADAMTS13 activity (n=56).

We stratified ADAMTS13 activity in patients whose diagnosis was known with the TTP group having the lowest mean of 13.1 + 13.6% (n=15). Patients without TTP had a mean ADAMTS13% of 65.5 + 23.02% (n=5); samples of atypical hemolytic uremic syndrome (aHUS) patients (n=2) had a mean of 84.4 + 28.8%. One patient with malignant hypertension (HTN) and one unknown had ADAMTS13 activity levels of 42.8% and 18.7%, respectively.

Conclusion: Although all patients were suspected of TTP based on their clinical symptoms, only an ADAMTS13 activity test can reliably confirm who has TTP. Our preliminary results do support the use of ADAMTS13 assay to rule out other thrombotic disorders masquerading as TTP. We are yet to receive all pertinent information about the patient’s samples to know at what stage of treatment samples were obtained. However, TTP samples had the lowest mean ADAMTS13 activity compared to HIT, PF4, ITP, and TMA, consistent with decreased levels of plasma ADAMTS13 activity in TTP patients.
Original languageAmerican English
StatePublished - 16 Feb 2023
EventOklahoma State University Center for Health Sciences Research Week 2023 - Oklahoma State University Center for Health Sciences, 1111 W. 17th street, Tulsa, United States
Duration: 13 Feb 202317 Feb 2023


ConferenceOklahoma State University Center for Health Sciences Research Week 2023
Country/TerritoryUnited States
Internet address


  • Hematology
  • ADAMTS13
  • plasma
  • thrombotic disorders
  • blood disorders


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