Coagulation laboratory tests
Platelet aggregation studies

Topic Completed: 1 November 2012

Revised: 7 January 2019, last major update November 2012

Copyright: (c) 2002-2016,, Inc.

PubMed Search: Platelet aggregation studies [title]

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Definition / general | Laboratory
Cite this page: Parsons J. Platelet aggregation studies. website. Accessed June 7th, 2020.
Definition / general
  • 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
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