Heparin-induced thrombocytopenia with very high antibody titer is associated with slower platelet recovery and higher risk of thrombosis

Heparin-induced thrombocytopenia (HIT) is a prothrombotic disorder mediated by platelet-activating antibodies targeting platelet factor 4 (PF4) and heparin complex. A higher antibody titer is reflected in a higher optical density (OD) by enzyme-linked immunosorbent assay for heparin–PF4 antibodies. This single-institution retrospective study of 116 HIT patients examined the effect of heparin–PF4 OD on time to platelet recovery, vascular thrombosis, and in-hospital mortality. Patients were divided into 3 cohorts based on heparin–PF4 OD: cohort 1 had an OD ≥ 2 and ≤ 2.4, cohort 2 had an OD > 2.4 and ≤ 2.8, and cohort 3 had an OD > 2.8. A higher OD titer was associated with significantly increased time to platelet recovery when compared between cohorts 1 versus 2 (HR = 0.599, p = 0.0221) and 1 versus 3 (HR = 0.515, p = 0.0014), as well as an increased risk of thrombosis (79.4%—cohort 3 vs 53.8%—cohort 2 vs 46.1%—cohort 1, p = 0.04), but had no impact on mortality (2.62—alive vs 2.65—deceased, p = 0.7432). A higher OD titer can inform risk assessment and support decision-making in HIT patients; however, prospective studies are needed to further clarify the impact of heparin–PF4 OD on outcomes.