Observations on human platelet aggregation in native whole blood: synergism and sensitivity to aggregating agents in vitro.

Threshold sensitivity levels, as well as the synergistic effects of agonists for blood platelets have been evaluated by impedance aggregometry using whole blood without anticoagulation. Platelet aggregation was studied using adenosine diphosphate (ADP), epinephrine, and thrombin. Threshold responses to ADP, epinephrine, and thrombin were observed at lower concentrations in diluted native whole blood (NWB) than reported values for citrated whole blood, and appear to be similar to those of citrated platelet rich plasma (PRP). Potentiation of aggregation occurred when both ADP and epinephrine, or epinephrine and thrombin but not ADP and thrombin were present in combination. Synergism between agonists thus is similar but not identical to that of PRP, and NWB appears to provide a sensitive system with a more physiologic milieu than other in vitro aggregation systems.