Diagnosing heparin-induced thrombocytopenia: The need for accuracy and speed.

Heparin-induced thrombocytopenia (HIT) is a prothrombotic condition resulting from pathogenic antibodies to complexes of heparin and platelet factor 4 (PF4). The diagnosis of HIT can be challenging due to the widespread use of heparin and the frequency of thrombocytopenia in hospitalized patients. Laboratory testing for HIT typically includes an immunoassay to detect antibodies to PF4-heparin and a functional assay. Current HIT diagnostic algorithms recommend using the 4Ts score to determine the need for HIT laboratory testing. Automated calculation of HIT clinical prediction scores in the electronic health record may improve the identification of patients who should undergo HIT testing. Another challenge in the management of patients with suspected HIT is the turnaround time of the laboratory testing needed to confirm the diagnosis. Due to the high daily thrombotic risk of HIT, clinicians must treat patients with intermediate to high pretest likelihood of HIT empirically while awaiting the test results. Treatment for HIT often involves alternative anticoagulants that lack reversal agents, which may increase bleeding risk, prolong hospital stays, and increase costs for patients suspected of having HIT. Rapid immunoassays hold promise to improve the speed of HIT diagnosis. These assays must retain a very high sensitivity for this "can't miss" diagnosis, yet have sufficient specificity to be of diagnostic value. A Bayesian approach has been proposed using two rapid immunoassays in succession, which decreased analytic turnaround time to 60 minutes. Such an approach has the potential to be a much-needed clinical advance in improving accuracy and speed in the diagnosis of HIT.