Platelet Function Testing: Aggregometry and Lumiaggregometry

Extract

Platelets are central to primary hemostasis, and platelet disorders manifest themselves with mucocutaneous (systemic) bleeding: petechiae, purpura, epistaxis (nosebleed), hematemesis (vomiting blood), and menorrhagia (uncontrolled menses). The accompanying article by Dr. Larry Brace entitled “Thrombocytopenia” describes the most common conditions in which platelet counts fall to hemorrhagic levels. In “Qualitative Platelet Disorders”, Dr. Brace describes hemorrhagic disorders in which platelet count is normal or mildly reduced but function is compromised. This introductory article describes platelet aggregometry and lumiaggregometry, the current laboratory means for diagnosing platelet disorders. These articles are adapted from chapters 43, 44, and 45 of Rodak BF, Fritsma GA, and Doig K, editors. Hematology: Clinical Principles and Applications, 3^rd ed. Philadelphia: Saunders; In press. The textbook is due for publication March, 2007.

To determine the cause for mucocutaneous bleeding, a platelet count is performed, and the blood film is reviewed before beginning platelet function tests (see “Thrombocytopenia”).¹ Functional platelet abnormalities are suspected when bleeding is present but the platelet count exceeds 50,000/μL (see “Qualitative Platelet Disorders”). Acquired platelet defects are associated with liver disease, renal disease, myeloproliferative disorders, myelodysplastic syndromes, myeloma, and drug therapy. Hereditary platelet functional disorders are less common, but provide models for physiological study. Platelet morphology is often a clue; Bernard-Soulier syndrome is associated with mild thrombocytopenia and large, gray platelets. The presence of large platelets with an elevated mean platelet volume often indicates rapid platelet turnover, such as in immune thrombocytopenic purpura or thrombotic thrombocytopenic purpura. Giant or bizarre platelets are seen in myeloproliferative…

ABBREVIATIONS: AA = arachidonic acid; ADP = adenosine diphosphate; ATP = adenosine triphosphate; GP = glycoprotein; NSAID = nonsteroidal anti-inflammatory drug; PAR = protease-activatable receptors; PRP = platelet-rich plasma; VWF = von Willebrand factor.