Platelet Function Assays: Diagnosis & Tests Menu

Diagnosis of Platelet Function Assays

A bleeding or clotting disorder, called “bleeding diathesis,” is an abnormal hemostatic process. It can be a delay in clotting after injury, leading to hemorrhage, or a tendency to develop thrombi in blood vessels. Disorders of platelets is a major consideration in a bleeding diathesis, and the diagnosis of abnormal platelet function begins with an in-depth history and a thorough physical exam.

A bleeding history can reveal problems a patient may have had with bleeding after surgery, tooth extractions, and in women, menstrual flow. The patient can be asked about bloody urine, blood in the stool, or persistent bleeding beyond what was expected after minor trauma. Aspirin consumption, the most common cause of platelet dysfunction, can be identified. A history of transfusions is obtained. Family history of clotting or bleeding abnormalities can identify those at risk for congenital clotting dysfunction.

The physical exam can readily identify suspicious, unprovoked (by history) bruises (“ecchymoses”), petechiae (small hemorrhagic blood spots under the skin), or “splinter hemorrhages” (small bloody streaks under the nails). Large, spreading soft tissue hematomas can be documented.

Initial Testing

  • Platelet counting: From a peripheral smear of blood on a slide can allow manual counting, totaling how many platelets are there in one high-power field of magnification; platelets can also be counted with an automated process that flags samples with unusual abundance or sparsity of platelets.
  • Bleeding time: Is determined by making a small cut and timing how long hemostasis takes. This tests the interaction of platelets with a blood vessel wall, but is invasive and uncomfortable.
  • Platelet Function Analyzer: commercially available, this has largely replaced the cumbersome bleeding time test.
  • Prothrombin time (PT): Tests one of the pathways (extrinsic) of the clotting cascade which platelets impact.
  • Activated partial thromboplastin time (APTT) tests another pathway, the intrinsic clotting cascade.
  • Genetic testing of blood DNA to identify gene mutations

Platelet Function Testing

  • Platelet Aggregometry: Platelet-rich plasma is the medium of free, circulating platelets which make it cloudy. When platelets aggregate together, this clumping clears portions of the plasma, allowing more light to pass through it (less cloudiness).
  • Whole Blood Aggregometry: The same as with plasma, but with whole blood.
  • Light Scattering methods: another version of evaluation via light transmission, using the light-scattering effects of clots vs free, circulating platelets.
  • Verify Now Assay: The latest technology in aggregometry.
  • Clot Signature Analyzer: Uses a tube of blood with holes that can reveal platelet clot “plugs” as a measure of platelet function.
  • Thrombotic Status Analyzer: Uses whole blood drawn into a small “capillary” tube to measure platelet activation via capillary tube occlusion.
  • Platelet Function Analyzer: a measure of the drop-in flow rate through a capillary tube as platelets form hemostatic plugs.
  • High Shear Filterometer: controlled pressure used to push blood through a filter and measure the time until the filter is blocked.

Diagnosis of inherited bleeding disorders, such as coagulation deficiencies, mutations, and platelet inhibition can be made from a battery of selected tests individualized for the patient.

Diagnosis of abnormal platelet function begins with an in-depth history and a thorough physical exam. A bleeding history can reveal problems a patient may have had with bleeding after surgery, tooth extractions, and in women, menstrual flow. The patient can be asked about bloody urine, blood in the stool, or persistent bleeding beyond what was expected after minor trauma. A history of transfusions is obtained. Family history of clotting or bleeding abnormalities can identify those at risk for congenital clotting dysfunction.

The physical exam can readily identify suspicious, unprovoked (by history) bruises (“ecchymoses”), petechiae (small hemorrhagic blood spots under the skin), or “splinter hemorrhages” (small bloody streaks under the nails). Large, spreading soft tissue hematomas can be documented.

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This information is provided by Vascular Health Clinics and is not intended to replace the medical advice of your doctor or healthcare provider. Please consult your healthcare provider for advice about a specific medical condition.

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