Inhibition of KKO and RTO by human HIT antibodies. Scattergram showing inhibition of model antibody (KKO or RTO) binding to PF4:H by human plasma containing anti-PF4 antibodies (ELISA positive). Pos denotes competition with antibodies from SRA-positive patients, and Neg denotes competition with antibodies from SRA-negative patients. Means ± SDs are shown (*P < .0001).