Critical importance of citrate--blood ratio in platelet aggregation studies.

The effects of citrate concentration on adenosinediphosphate-, epinephrine-, collagen-, and ristocetin-induced human platelet aggregation were investigated. Relatively small increments in citrate concentration markedly inhibited platelet aggregation by all three physiologic agents. The inhibitory effect was greatest on epinephrine-induced aggregation, and least on collagen-induced aggregation. Ristocetin-induced aggregation was not affected by excess citrate anticoagulation. These findings indicate the importance of controlling the citrate:blood ratio in clinical platelet aggregation studies and in the assessment of antiplatelet drugs.