Comparison of activation and antigen assays for HIT-IgG antibodies in patients who have undergone cardiac and orthopedic surgery.

Quantitative results of activation and antigen tests for HIT-IgG are shown for 3 clinical treatment settings: orthopedic–UFH (A), orthopedic–LMWH (B), and cardiac–UFH (C). Results are shown for all 744 patients. All antigen assay data are given quantitatively. For the activation assay results, samples that gave less than 20% serotonin release are as shown without reference to the actual quantitative result obtained (see box designated < 20%); quantitative data are given when the percentage serotonin release was 20% or more. Arrows indicate the data points corresponding to the 15 patients with HIT identified in these prospective studies.