Is the combination of two automated rapid assays for diagnosis of heparin-induced thrombocytopenia necessary?

Heparin-induced thrombocytopenia (HIT) is an immune-mediated condition characterized by a decrease in platelet count and an increased thrombotic risk. HIT event is caused by antiplatelet factor/heparin (PF4/H) antibodies that can activate the platelets. The diagnosis of HIT is based on a clinical evaluation and laboratory results. Aim of our study was to evaluate whether the combined use of two rapid assays for diagnosis of HIT provides a diagnostic advantage over the use of a single automate assay. We extracted from the laboratory informatic system all the determinations requested for the detection of antibodies against heparin/PF4 complexes from July 2020 to June 2024 (n. 229). In our laboratory, total antibodies against heparin/PF4 complex [HemosIL HIT-Ab-(PF4-H), Instrumentation Laboratory] and IgG Ab (HemosIL AcuStar HIT-IgG, Instrumentation Laboratory) are measured simultaneously with two different instruments. Two hundred six samples tested negative for both methods, 23 samples tested positive for at least one method and nine samples tested positive for both methods. The grade of concordance between the two assays shows a weighted Kappa of 0.536 (moderate agreement). No sample tested positive only for IgG-Ab. The sensitivity of HIT-Ab-(PF4-H) was 1, whereas the specificity was 0.95. For the HIT-IgG (PF4-H) method, sensibility and specificity were 0.77 and 1, respectively. Our results suggest that performing these two tests simultaneously does not provide additional useful information in patients with suspicion of HIT. The total Ab assay seems to be sufficient, as it shows higher sensitivity although at the expense of lower specificity.