Automated Chemiluminescent Assays Evaluated for Heparin-Induced Antibodies

Two recently introduced automated chemiluminescent assays for the detection of antibodies have been evaluated in the diagnosis of heparin-induced thrombocytopenia.

The performance of the two assays was compared with enzyme linked immunosorbent assays (ELISA) heparin-induced antibodies (HIA) tests for immunoglobulins IgG and IgAM.

Scientists at Ghent University Hospital (Belgium) collected citrated plasmas from 87 patients with clinical suspicion of heparin-induced thrombocytopenia (HIT) were analyzed with all four assays and with a functional confirmation assay. The Zymutest HIA IgG and HIA IgGAM assays (Aniara; West Chester, OH, USA) are micro-ELISAs, that take over two hours to perform, were used as the standard reference.

The fully automated quantitative chemiluminescent immunoassays, the HemosIL AcuStar HIT-IgG (Platelet Factor 4-Heparin, PF4-H), specific for IgG anti-PF4/H antibodies, and the HemosIL AcuStar HIT-Ab (PF4-H), detecting IgG, IgM and IgA anti-PF4/H antibodies are products of Instrumentation Laboratory (Bedford, MA, USA). They provide enhanced detection of HIT antibodies in specialty and hospital hemostasis laboratories. Unlike existing manual processes, the ready-to-use, cartridge-based assays offer results in approximately 30 minutes.

The sensitivities of all assays were 100%. The Acustar HIT-IgG assay showed 85% specificity compared to the 73% for the HIT-Ab assay using the manufacturer’s cutoffs. Specificities of all assays, except for the AcuStar HIT-IgG, could be significantly improved when altering the cutoff. Titers were significantly higher for the HIT-Ab assay compared with the HIT-IgG assay. This was also the case for the patients with confirmed HIT indicating that the cutoff of 1.0 Optical Density (OD) for both AcuStar assays, as proposed by the manufacturer, can be adapted for the AcuStar Hit-Ab assay resulting in an increased specificity.

Chemiluminescent technology provides analytical excellence through an expansive working range for high sensitivity and precision allowing clinicians to make timely, well-informed therapeutic decisions. In addition, the Acustar HIT precalibrated reagent cartridges offer significant time- and cost- efficiencies. The study was published in the August 2012 edition of the International Journal of Laboratory Hematology.

Related Links:
Ghent University Hospital
Aniara
Instrumentation Laboratory