Accuracy of heparin-induced platelet aggregation test for the diagnosis of heparin-induced thrombocytopenia

Introduction: Whereas the utility of washed platelet assays such as the heparin-induced platelet activation test (HIPA) for the diagnosis of heparin-induced thrombocytopenia (HIT) is regarded as high, the performance of simpler assays such as the heparin-induced platelet aggregation test (PAT) is still elusive. Using well-characterized samples of a large cohort study, we aimed to assess the diagnostic accuracy of PAT for the diagnosis of HIT. Material and methods: One-hundred twenty-two immunoassay-positive serum samples of a previous, prospective single-center cohort study including consecutive patients with suspected HIT (n = 1291) were used. HIPA was determined as reference gold standard; samples were previously analyzed using PAT as well as polyspecific platelet factor 4/heparin enzyme-linked immunosorbent assay (ELISA). 4Ts score was calculated using the patient documentation. Diagnosis of HIT was defined as a positive HIPA, which is a positive reaction in 2 out of 4 donor platelets within 30 min. Results: HIT was diagnosed in 39 out of 122 patients corresponding to a prevalence of 32%. Median optical density (ELISA) was 2.8 (inter-quartile range 2.3, 3.0) in patients with HIT and 0.7 (0.5, 1.3) in patients without HIT. PAT was positive in 27 out of 39 HIT patients and it was negative in 83 out of 83 HIT-negative patients. Thus, the sensitivity of PAT for the diagnosis of HIT was 69% (95% confidence interval 52%, 83%) and the specificity 100% (96%, 100%). Conclusions: Our results demonstrate that PAT is a valuable test to confirm HIT but cannot be applied to rule-out HIT in clinical practice.