Evaluation of platelet aggregability by computerised probit analysis

The concentration of 5'-adenosine diphosphate (ADP) required to produce fifty percent of the estimated maximal response (ADP EC₅₀) was determined by computerised probit analysis. This correlated directly and significantly with the minimum concentration of ADP required to produce (i) a biphasic aggregation response (ADP_Biphasic); and (ii) a maximal aggregation response exceeding 50% (ADP_{PA > 50}). Platelet aggregability was evaluated in 70 subjects consisting of 18 patients with coronary heart disease (CHD), 13 with ischemic cerebrovascular disease (CVD), 18 with rheumatoid arthritis (RA) and in 21 healthy controls. The mean (SEM) values of EC₅₀ were slightly but not significantly decreased (hence platelet aggregability increased) in patients with CHD (2.58 +− 0.36 μmoles/L) and RA (2.23 +− 0.36 μmoles/L) as compared with controls (2.94 +− 0.34 μmoles/L); and slightly elevated in patients with ischemic CVD (3.39 +− 0.34 μmoles/L). The mode values of ADP_{PA > 50} were also less in the CHD and RA groups (2 μmoles/L) as compared with the controls (4 μmoles/L); in the CVD group the mode was 4 μmoles/L. The mode values of ADP_Biphasic were however the same in all the four groups, namely 2 μmoles/L.