Platelet Count

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Latest Edit: Hector 2014-03-24 (EDT)

See Also Lab Tests

The platelet count is an actual count of the number of platelets in blood. It is part of the complete blood count and is used in evaluation of petechiae (small hemorrhage), spontaneous bleeding, increasingly heavy menses, or thrombocytopenia.[1], [2]


Platelets are formed in the bone marrow from megakaryocytes. They are small, round, nonnucleated cells whose main role is maintenance of vascular integrity including blood clotting. Platelets lasts roughly a week in the peripheral blood.

Patient Preparation

  • Fasting is not required.

Interfering Factors:

  • Living in high altitudes may cause increased platelet levels.
  • Strenuous exercise may cause increased levels.
  • Decreased levels may be seen before menstruation.
  • Drugs which may cause increased levels include estrogens and oral contraceptives.
  • Drugs which may cause decreased levels include acetaminophen, aspirin, chemotherapeutic agents, chloramphenicol, colchicine, H2-blocking agents (cimetidine, Zantac), hydralazine, indomethacin, isoniazid, quinidine, streptomycin, sulfonamides, thiazide diuretics, and tolbutamid.

Clinical Implications

Platelet counts are typically used to evaluate bleeding, hemorrhage, blood clotting disorders, and thrombocytosis.

High levels indicate: High levels indicate thrombocytosis which may be associated with:

Low levels indicate: Low levels indicate thrombocytopenia which may be associated with:

Associated Tests

Related tests include platelet aggregation, platelet antibody, bleeding time, mean platelet volume, clot retraction.


  1. Pagana Kathleen D, Pagana Timothy J (2006) Mosby's Manual of Diagnostic and Laboratory Tests, Mosby.
  2. Weatherby Dicken, Ferguson Scott (2002) Blood Chemistry and CBC Analysis: Clinical Laboratory Testing from a Functional Perspective, Bear Mountain.