Aim: Heparin-induced thrombocytopenia (HIT) is a severe complication of heparin therapy, due to IgG antibodies binding to platelet factor 4 (PF4) and heparin complexes. These complexes cause platelet activation and subsequent aggregation, contributing to venous and arterial thromboses. Diagnosis includes the 4T score, based on clinical presentation and laboratory findings. This study evaluated the HemosIL® AcuStar HIT IgG chemiluminescent immunoassay against the HPIA IgG ELISA and STic Expert® HIT methods.
Method: The HemosIL® AcuStar HIT IgG chemiluminescent immunoassay detects IgG antibodies directed against PF4 when complexed with heparin. Magnetic particles, coated with PF4 and complexed to polyvinyl sulfonate, capture PF4-Heparin (PF4-H) antibodies. Added isoluminal-labelled anti-human IgG antibody tracer subsequently binds to the PF4-H antibodies, and a luminescent reaction is initiated by the addition of a trigger reagent. Emitted light is measured optically as relative light units and is directly proportional to the PF4-H IgG antibody concentration. AcuStar HIT IgG was performed on thawed citrated platelet poor plasma stored at -80ºC, from patients who had previously been tested for IgG PF4-H antibodies using HPIA IgG ELISA and STic Expert® HIT assays. Results obtained from the confirmatory ‘gold standard’ serotonin release functional assay (SRA) were also evaluated.
Results: 44 patients were tested (26 positive and 18 negative by ELISA) using the AcuStar HIT IgG assay with a sensitivity and specificity of 92% and 100% respectively. Sensitivity is further improved by optimising the diagnostic cut-off provided by the manufacturer. The automated AcuStar produced a result in approximately 40 minutes, compared to 4 hours using the manual ELISA technique.
Conclusion: The AcuStar HIT IgG assay is diagnostically comparable to the HPIA IgG ELISA method. However, the AcuStar assay has the advantage of a decreased cost per test with a reduction in workload and result turnaround time.