Addition of Ristocetin to formalin-fixed platelets suspended in diluted PPP induces
a marked increase in turbidity which is not caused by platelet shape change but by
the formation of microaggregates. If diluted PPP of patients with severe von Willebrand's
disease is used, only an initial increase in turbidity and no further decrease is
observed without any form variation of the platelets but again with formation of many
microaggregates. In normal PRP diluted with buffered EDTA, ADP induces an increase
in turbidity without further changes in optical density. Simultaneously platelets
immediately change their shape with formation of pseudopodes and sphering but at the
same time also microaggregates appear. Shape change and microaggregate formation can
also be observed after the addition of Collagen to undiluted PRP which is followed
by the formation of large aggregates and a decrease in optical density. Increase in
optical density in undiluted PRP is not a specific indicator of platelet shape changes.
Microaggregates can alone or partially be responsible for these changes. For the evaluation
of platelet shape changes but also for the estimation of microaggregate formation
microscopic methods are preferred.
Key words
Platelet shape change - Aggregation - Microaggregate formation - Formalin-fixed platelets
- Optical density
