Concentration dependent inhibition of HIT serum-induced platelet aggregation by the ADP receptor antagonist AR-C66096. Platelets, 500 × 10⁹/L, were preincubated with various concentrations of AR-C66096 or thromboxane receptor inhibitor Daltroban at 37°C for 2 minutes before stimulation with HIT serum no. 1 or 100 nmol/L AA. HIT serum no. 1: Mean % aggregation with control buffer was 55 ± 6%. AA: Mean % aggregation with control buffer was 53 ± 4% (mean ± SD, n = 3). HIT sera no. 2 and 3 and platelet suspensions from donors other than in the case of HIT serum no.1 gave similar results.