Combination of 2 Quantitative Immunoassays and Clinical Score Algorithm to Reduce False-Negative Results in Heparin-Induced Thrombocytopenia: Prevalence Study of Mauriziano Hospital in Turin, Italy.

Background: Heparin-induced thrombocytopenia (HIT) is a serious adverse effect of heparin treatment caused by platelet-activating anti-platelet factor 4 (PF4)/heparin antibodies. Accurate diagnosis of HIT is essential but remains challenging. The aim of our study was to explore the performance of our optimized diagnostic laboratory algorithm, based on Chemiluminescence (CliA) and ELISA immunoassays, on suspected HIT patients. The study compared the prevalence of HIT diagnosis in A.O. Mauriziano with the literature.

Methods: 163 consecutive patients were investigated for suspected HIT with CliA HemosIL Acustar HIT-IgG, Werfen. HIT was ruled out in all patients with CliA <0.13 U/mL. All patients with CliA >0.13 U/mL were further investigated with Zymutest-HIA anti-PF4 IgG ELISA immunoassay. In these patients, HIT was ruled out on the combination of CliA between 0.13 and 1.0 U/mL followed by ELISA assay <0.300 OD. HIT was ruled in patients whose plasma tested positive or doubtful with CliA and positive with ELISA immunoassay and confirmed positive with a platelet aggregation test (PAT). Suspicion of HIT was revealed with clinical 4Ts score or recent suggestive anamnestic history.

Results: Our diagnostic algorithm ruled out HIT diagnosis in 144/163 patients (88%) and predicted a positive PAT in 5/19 (26%) of CliA positive (4/5) or ELISA positive and CliA doubtful (1/5) patients.

Conclusions: Our prevalence was 3.1%, comparable with the literature. The approach combining 2 quantitative immunoassays' (CliA and ELISA) results and 4Ts score probability was able to rule out the diagnosis within 1 h in 66% of patients with suspected HIT and within 24 h in 88% of patients. In the remaining 12% of cases, management decisions have to be based on individualized judgment while awaiting functional confirming results (48-72 h).