Heparin-induced thrombocytopenia: evaluation of IgG and IgGAM ELISA assays

Heparin-induced thrombocytopenia (HIT) is a rare complication of heparin therapy resulting from antibody production to platelet factor 4 and heparin complexes (H-PF4).

We have evaluated four enzyme-linked immunosorbent assay (ELISA)-based screening tests to identify the best assay(s) with the highest specificity but without underdiagnosis of HIT. As functional assays are difficult to perform, ELISAs are useful to provide clinicians with a timely answer. Over a 10-month period, all samples (N=107) referred to our laboratory were tested for HIT antibodies using four commercially available ELISA kits, two detecting IgG/A/M anti-H-PF4 antibodies and the other two IgG specific.

Twenty-eight samples were positive by at least one assay; IgGAM ELISAs were found to be more sensitive with 24 samples positive by Asserachrom IgGAM and 23 by Zymutest IgGAM. Only 18 samples were positive by GTI-PF4-IgG and Zymutest IgG. The gold standard serotonin release assay (SRA) was used as a confirmation assay, and 11/28 samples tested positive. All these SRA-positive samples were positive by all four assays. None of the IgGAM-only-positive samples was found to be positive by SRA suggesting a better specificity for the IgG-only assays.

Our data strongly support the use of IgG-only assays for the detection of HIT antibodies.