How is platelet aggregation measured in the workup of platelet disorders?

Updated: Nov 30, 2019
  • Author: Perumal Thiagarajan, MD; Chief Editor: Srikanth Nagalla, MBBS, MS, FACP  more...
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Answer

Answer

Platelet aggregation is measured by turbidimetric methods. When platelets aggregate, the opalescent suspension of platelet-rich plasma becomes clearer and allows more light transmission. The extent of aggregation is determined by measuring the increase in light transmission.

Small doses of ADP (< 1 µmol) induce a reversible form of platelet aggregation (primary wave), unaccompanied by thromboxane synthesis or release of intraplatelet ADP. However, with increasing doses of ADP, sufficient stimulation of platelets occurs and leads to the release of intraplatelet ADP and the synthesis of thromboxane A2 from arachidonic acid, thus resulting in more pronounced irreversible aggregation (secondary wave).

Ristocetin induces platelet aggregation by inducing von Willebrand protein binding to the platelet GP Ib complex.

Platelet aggregation tests are useful in distinguishing different disorders of platelet function. They are also particularly useful in the diagnosis of von Willebrand disease, in which ristocetin-induced platelet aggregation is defective.


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