Heparin-induced thrombocytopenia

Abstract

Heparin-induced thrombocytopenia (HIT) is a prothrombotic disorder caused by antibodies that recognize complexes of platelet factor 4 (PF4) and heparin. HIT is frequently considered in the differential diagnosis of thrombocytopenia occurring in patients on heparin therapy. HIT is a challenging diagnosis because of routine heparin use in hospitalized patients, the common occurrence of thrombocytopenia, and high rates of anti-PF4/heparin seroconversions in patients treated with heparin. Our diagnostic approach to HIT is presented here, underscoring critical elements of clinical and laboratory evaluation.

Figure 1. Evolution of the HIT immune response in relation to clinical manifestations

12 patients with HIT (■) and 36 control patients who were PF4/H seropositive but did not have HIT (□) were monitored after orthopedic surgery for PF4/H antibodies, thrombocytopenia, and thrombosis. The time course of PF4/H seroconversions are shown on the x-axis and OD levels are shown on the y-axis. The difference in OD between the HIT patients and the seropositive non-HIT controls was statistically significant (P < 0.05 by nonpaired t test). Four key events for the 12 patients with HIT are shown: first day PF4/H antibody was detectable, onset of HIT-related fall in platelet count, fall in platelet count ≥ 50%, and thrombotic event. These events are shown as medians (small black squares within rectangles), interquartile ranges (length of open rectangles), and ranges (ends of thin black lines). Adapted from with copyright permission from publisher.

Figure 2. Diagnostic algorithm

Our diagnostic approach for HIT using clinical and laboratory evaluation. *Based on reference †Based on reference