HEPARIN-INDUCED THROMBOCYTOPENIA - IGG BINDING TO PF4-HEPARIN COMPLEXES IN THE FLUID-PHASE AND CROSS-REACTIVITY WITH LOW-MOLECULAR-WEIGHT HEPARIN AND HEPARINOID

Early diagnosis of heparin-induced thrombocytopenia (HIT) is essential to reduce morbidity and mortality. We report an enzyme immunoassay wh ich detects the binding of HIT IgG to PF4-heparin in the fluid phase. Our fluid phase assay produces consistently low background and can det ect low levels of anti-PF4-heparin. It is suited to testing alternativ e anticoagulants because, unlike in an ELISA, a clearly defined amount of antigen is available for antibody binding. We were able to detect anti-PF4-heparin IgG in 26/28 (93%) HIT patients. We investigated cros s-reactivity of anti-PF4-heparin antibodies with PF4 complexed to alte rnative heparin-like anticoagulants. Low molecular weight heparins cro ss-reacted with 23/26 (88%) of the sera from HIT patients while half o f the HIT sera weakly cross-reacted with PF4-danaparoid (Orgaran). The thrombocytopenia and thrombosis of most of these patients resolved du ring danaparoid therapy, indicating that detection of low affinity ant ibodies to PF4-danaparoid by immunoassay may not be an absolute contra indication for danaparoid administration.