ADAMTS13 Overtesting in Hospitalized Patients with Suspected TTP: A Retrospective Study

Introduction: Acquired thrombotic thrombocytopenic purpura (aTTP) is a life-threatening disease characterized by thrombotic microangiopathy with an untreated mortality rate of >90%. Diagnosis relies on ADAMTS13 testing, in-house testing is reported to cost $4732/test. Average cost of treating typical aTTP episode with caplacizumab is $270,000. Validated scoring systems like PLASMIC/French-TMA models in conjunction with clinical evaluation may help with early diagnosis and avoid unnecessary testing.

Methods: We identified 68 unique hospitalized adult patients with no history of TTP who had ADAMTS13 activity checked between 12/2019 and 04/2022. Collected data included demographics, COVID status, location where test was ordered, test results, time for test to return, whether peripheral smears were ordered, evidence of PLASMIC score documentation and final diagnosis. Descriptive statistics were utilized to report data as means and percentages.

Results: Median age was 52±17 years with an equal distribution of males (34/68, 50%) and females (34/68, 50%). 54/64 (84.4%) patients had a COVID negative status. 35/68 (51.5%) tests were ordered in the intensive care unit and the remaining 33/68 (48.5%) tests were ordered on regular floor patients. 65/68 (95.6%) ADAMTS13 tests returned negative. Mean time for ADAMTS13 to return was 2.67±1.51 days. While 52/68 (76.5%) had a peripheral smear ordered, 51/68 (75%) had no documentation of PLASMIC score. Retrospectively calculated PLASMIC scores revealed 31 (45.6%) with low-risk, 22 (32.3%) with intermediate-risk and 15 (22.1%) with high-risk. Only 5/68 (7.4%) were ultimately diagnosed with TTP and 15/68 (22%) in the non-TTP category were treated with PLEX and/or steroids before results were available. DIC, Sepsis, COVID, alcohol toxicity/cirrhosis and ITP were final diagnoses in 40/68 (58.8%) patients (Table 1).

Conclusions: There is a pattern of ADAMTS13 overtesting in the hospitalized setting. PLASMIC and French-TMA scoring models offer high sensitivity/specificity and should be used to enhance clinical judgement and guide initial management. A high index of suspicion, physician education about expensive tests, EMR pop-ups as deterrents can help with risk stratification to curb unnecessary testing. In-house ADAMTS13 testing offers rapid results and thus reduce plasma utilization as our study revealed 15/68 (22%) non-TTP patients were treated for TTP before results arrived.

Master:Cardinal Health: Membership on an entity's Board of Directors or advisory committees; Aptitude health: Membership on an entity's Board of Directors or advisory committees; curio sciences: Membership on an entity's Board of Directors or advisory committees; Blue Bird Bio: Current holder of stock options in a privately-held company; Toxicity: Current holder of stock options in a privately-held company; Gilead: Current holder of stock options in a privately-held company; Jasper: Current holder of stock options in a privately-held company.