Platelet Function Analysis (PFA-100) Test

The PFA-100 is a screening test for platelet dysfunction. In this test, citrated whole blood is aspirated through a stainless steel capillary under vaccuum. This generates physiological shear stresses which activate the platelets.

The activated platelets are then passed through a membrane with a central aperture. The membrane is coated with collagen, and with one of two platelet agonists (epinephrine or ADP). The platelets adhere to the collagen and aggregate in response to the collagen and epinephrine (or ADP). Eventually, adhesion and aggregation proceed to a point where the central aperture becomes occluded and blood flow through the membrane stops. This is known as the Closure Time (CT) and is reported in seconds.

The test is run first with the collagen/epinephrine (CEPI) membrane. If an abnormal result is obtained, the test is repeated with the collagen/ADP (CADP) membrane. Interpretation of results is as follows:

• Normal CEPI result suggests normal platelet function;
• Abnormal CEPI closure with a normal CADP result is most likely due to aspirin ingestion. However, platelet storage pool or release defects may give a similar pattern;
• Abnormal CEPI and CADP results indicate abnormal platelet function.

Please note that low platelet counts (typically <70,000/cmm) and low hematocrit (<25%) may also prolong closure time in the PFA-100. It is a particularly sensitive screening test for von Willebrand's Disease and the CT is usually prolonged when the vWF activity is less than 40%. The PFA-100 test should not be used to detect or monitor the effects of Plavix.

The Hemostasis and Thrombosis Laboratory was one of the first centers in the United States to implement the PFA-100 as a routine platelet function screening test. We also offer full platelet aggregation and release studies for the complete evaluation of the patient with a possible platelet function defect.