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Coagulation laboratory tests

Platelet aggregation studies

Reviewer: Jeremy Parsons, M.D. (see Reviewers page)
Revised: 10 February 2013, last major update November 2012
Copyright: (c) 2002-2013, PathologyOutlines.com, Inc.


● Used to assess platelet function if a familiar bleeding disorder is suspected, but the PT, PTT, platelet count and von Willebrand tests are normal (which is unusual)
● May include platelet responses to adenosine diphosphate (ADP), epinephrine, collagen and arachidonic acid
● Agglutination with ristocetin may also be assessed
● Usually 60% or more platelets aggregate with the above agonists, but not spontaneously; aggregation is decreased in newborns (Br J Haematol 1988;68:53)
● Note: testing is labor intensive and must be scheduled in advance because a normal control must be drawn simultaneously
● A platelet function assay (e.g. PFA-100) may be used to assess platelet function; although easier to perform, it is not as robust as platelet aggregation and must be interpreted with caution

Hereditary disorders:
● Consider in patients with bleeding histories, no obvious acquired cause, but abnormal platelet aggregation study repeated at least once, same abnormality in family members
● May be a platelet storage pool disorder (deficiency in alpha or dense platelet granules), Glanzmann thombasthenia (deficiency of platelet glycoprotein IIb/IIIa, reduced aggregation by all agonists except ristocetin) or Bernard-Soulier disease (deficiency of platelet glycoprotein Ib, causes decreased ristocetin-induced aggregation only)


● Aggregometry with platelet-rich plasma to measure optical transmission or electric impendence (J Thromb Haemost 2009;7:1029)
● Whole blood aggregation with a lumiaggregometer can measure both aggregation and ATP release
● Abnormalities are often due to medications (aspirin - affects arachidonate aggregation; other platelet-inhibiting agents); also uremia, monoclonal gammopathy and myeloproliferative disorders

End of Coagulation > Coagulation laboratory tests > Platelet aggregation studies

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