Diagnosing heparin-induced thrombocytopenia in mechanical circulatory support device patients

Background: Mechanical circulatory support device (MCSD) patients with positive heparin-induced thrombocytopenia (HIT) screening pose a unique challenge, as clinicians must make rapid decisions about their anticoagulation and whether they can safely undergo cardiopulmonary bypass. We identified screening practices at our institution and other institutions nationwide that differed from American Society of Hematology (ASH) guidelines. This discovery prompted a data review to confirm the applicability of guidelines to this unique population and to highlight complications of "gestalt" screening.

Methods: Our study included MCSD patients with HIT testing from April 2014 to August 2020. We evaluated 510 PF4 IgG ELISA results.

Results: HIT was confirmed in 4.2% of patients. There was an increased prevalence of HIT in patients with nondurable (5.3%) vs durable devices (2.9%) or those in the preimplantation setting (1.3%), however this difference was not statistically significant (p = 0.26). None of the patients with a low probability 4T Score had HIT. All patients with a high probability 4T Score and PF4 immunoassay OD >2.0 had HIT. False positive results occurred in 22% of assays ordered for patients with a low probability 4T Score. Twelve patients with a low probability 4T Score and a false positive immunoassay were switched to a direct thrombin inhibitor (DTI) while awaiting confirmatory results. Two patients experienced clinically significant bleeding after conversion to a DTI. An organ was refused in one patient with false positive HIT screening.

Conclusions: Our findings demonstrate that an opportunity exists to improve clinical outcomes by re-emphasizing the utility of established guidelines and highlighting their safe use in the MCSD patient population.