Factors affecting the size distribution of platelet aggregates formed in whole blood
were measured using an electronic particle counter. Lysis of red cells after dilution
of blood for analysis allows detection of smaller aggregates without altering aggregate
measurement. Differences in platelet response to increasing concentrations of ADP
are detected by an increase in the mean size of platelet aggregates while the total
volume of aggregates varies linearly with the volume of available platelets (r = .99).
The mean aggregate size varies directly with the total volume of aggregates formed
(r = .99). Mean aggregate size is inversely related to the packed red cell volume.
As the reactivity of platelets is reduced by incubation with aggregation inhibitors
at increasing concentrations, the mean size of aggregates becomes smaller, followed
by a decrease in the total volume of aggregates. The total volume and mean size of
aggregates formed after incubation with collagen and epinephrine, but not ADP, increases
with time after venepuncture.
Keywords
Blood platelets - Platelet aggregation
