Summary
The Wu and Hoak method for determining circulating platelet aggregates has poor reproducibility;
problems have been reported with the composition of the buffer systems, haemolysis,
the effects of blood collection technique and a divergence of the platelet aggregate
ratio in blood for healthy donors from the theoretical value of 1. Our investigations
suggest that the original technique is highly operator-dependent, especially the collection
of blood and the method of counting platelets after centrifugation. We describe an
improved modification of the Wu and Hoak technique; a new buffer system has been developed
and the proportion of blood in the buffered EDTA and buffered EDTA- formalin solutions
has been altered to obtain platelet rich plasma. The platelet aggregate ratio (PAR)
by this modified method for healthy donors in two different studies was 0.97 ± 0.02
and 0.98 ± 0.01 respectively. Finally, the principle of Wu and Hoak was used to measure
accurately platelet adhesion, without the role of platelet-platelet interactions (aggregation).
Platelet adhesion and aggregation were then used to evaluate the thrombogenicity of
various artificial surfaces, including silicone rubber and polytetra- fluoroethylene
(PTFE) vascular grafts.
Keywords
Platelet aggregation - Adhesion - Artificial surfaces
