Normal standards of in vitro induced platelet aggregation.

Measurement of in vitro induced platelet aggregation by turbidimetric method is a very important investigative tool when patients are evaluated for bleeding diasthesis due to possible underlying platelet functional disorders. As commercial controls are not available, it is important that each laboratory establishes its own normal pattern of platelet aggregation induced by standard aggregating agents. The aggregation curves in terms of maximal % aggregation, Vmax and lag time in 50 normal Chinese controls are reported. The final concentrations of the aggregating agents used, namely adenosine diphosphate, adrenaline, collagen and ristocetin, are 20 microM, 10 microM, 0.2 mg/ml and 1.0 mg/ml, respectively. 20% of the controls had either no aggregation or only primary aggregation with adrenaline. Lag time by collagen-induced aggregation is significantly longer, but other parameters of platelet aggregation by adenosine diphosphate, adrenaline and collagen in Chinese are comparable to one reported control study. The maximal % aggregation induced by ristocetin in Chinese does not differ significantly from the reported values in whites but is significantly higher than in Blacks at a concentration of 1.0 mg/ml. Interpretation of platelet aggregometry in patients with bleeding tendency should be based on the normal patterns established from a group of normal controls in each laboratory rather than by comparison with a single control alone.