Combination of 4Ts score and PF4/H-PaGIA for diagnosis and management of heparin-induced thrombocytopenia: prospective cohort study

Rapid exclusion of heparin-induced thrombocytopenia (HIT) is needed to determine which patients can continue to receive heparin. In this prospective management study, 526 participants had a 4Ts score, rapid particle gel immunoassay (platelet factor 4/heparin [PF4/H]-PaGIA), and serotonin-release assay (SRA) performed. While awaiting SRA results, participants with a low 4Ts score (irrespective of PF4/H-PaGIA result) or intermediate 4Ts score plus a negative PF4/H-PaGIA result received prophylactic doses of danaparoid or fondaparinux; all others received therapeutic doses of nonheparin anticoagulants. The primary outcome was the frequency of management failures defined as HIT-positive participants with a low 4Ts score (irrespective of PF4/H-PaGIA result) or intermediate 4Ts score plus negative PF4/H-PaGIA result. Six participants (1.1%; 95% confidence interval [CI], 0.2-2.1%) were management failures. A negative PF4/H-PaGIA result reduced the pretest probability of HIT from 1.9% to 0% (95% CI, 0-1.3%), 6.7% to 0% (95% CI, 0-2.7%), and 36.6% to 0% (95% CI, 0-14.3%) in the low, intermediate, and high score groups, respectively. A positive PF4/H-PaGIA result increased the probability of HIT in the low score group to 15.4% (95% CI, 5.9-30.5). Thus, a low or intermediate 4Ts score plus negative PaGIA result excluded HIT, whereas any other combination of results justified the use of alternative anticoagulants until HIT could be excluded.