Specific quantification of heparin-dependent antibodies for the diagnosis of heparin-associated thrombocytopenia using an enzyme-linked immunosorbent assay.

In order to specifically detect heparin-dependent antibodies in patients with suspected heparin-associated thrombocytopenia (HAT), an adapted ELISA test was developed. Serum-platelet bindable IgG (SPb-IgG) were measured in the absence and in the presence of heparin in the sera from a/ 25 normal controls, 25 patients treated by heparin without thrombocytopenia, 29 thrombocytopenic patients not receiving heparin and b/ 12 patients with confirmed HAT. In the absence of heparin, the 12 HAT sera showed normal or elevated SPb-IgG levels (range = 10.4-36 Arbitrary Units or AU) as compared to healthy controls (8-17.1 AU). After coincubation of HAT sera with heparin (0.25, 0.50, 0.75, and 1 IU/ml), SPb-IgG levels were consistently elevated (range = 22.8-150 AU), and this increase in IgG binding (equal in mean to 200%) was always inhibited with 5 IU/ml of heparin. In contrast, a mean maximum increase in SPblgG levels of only 20% was registered in all control groups whatever the tested heparin concentration. Thus, this ELISA allows the specific diagnosis of HAT by demonstrating a serum IgG binding on platelets only in the presence of therapeutic concentrations of heparin.