Determination of heparin–platelet factor 4–IgG antibodies improves diagnosis of heparin‐induced thrombocytopenia

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Abstract
Only a few patients with heparin‐induced antibodies develop heparin‐induced thrombocytopenia (HIT). In this study, we investigated whether different immunglobulin classes can be used to differentiate between antibody‐positive patients with and without HIT. Four different patient populations were investigated: 32 patients with the immune type of HIT with thromboembolic complications, 13 patients with HIT without thromboembolism, 24 patients with heparin–platelet factor 4 (PF4) antibodies without clinical symptoms of HIT, and 20 heparin‐treated patients with thrombocytopenia caused by other reasons. In all patients the immunglobulin mixture of IgG, IgM and IgA, and the single immunglobulin classes of heparin–PF4 antibodies, were investigated. No significant differences between HIT patients with thromboembolic complications and patients with isolated HIT were found concerning the different immunglobulin classes. Antibody‐positive patients with HIT had significantly higher levels of IgG antibodies than those without HIT (P < 0·05), while they did not differ concerning IgM and IgA antibodies. By determining IgG antibodies, the specificity of the enzyme‐linked immunosorbent assay (ELISA) system was increased without loss of sensitivity. Heparin–PF4–IgG antibodies can identify patients at risk of developing life‐threatening HIT. Future ELISAs should only include this immunglobulin class, as the determination of the antibody mixture may lead to overestimation of HIT.