Platelet Function, Qualitative (PFA-100)
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On January 3, 2005 the PFA replaced the Bleeding Time for routine use at MCL. All orders for the Bleeding Time are automatically reflexed to the PFA and collections are scheduled to allow for processing within the four testing hour window. As with the Bleeding Time, the test will be performed M-F on the first shift.

The PFA offers several advantages over the bleeding time. The test is performed on a sodium citrate anticoagulated whole blood (standard blue top tube) and it assesses both the adhesion and aggregation of platelets. The test has been shown to be sensitive to von Willebrands syndrome, aspirin ingestion and other inherited and acquired platelet function anomalies. The Bleeding Time suffers from poor sensitivity and specificity and the literature indicates that it is not useful in preoperative screening. For example, the bleeding time is abnormal in only 35% of von Willebrands patients, whereas the PFA is reported sensitive in 91% of cases.

The PFA measures platelet function by simulating the adhesion and aggregation in vitro. Platelets first adhere and release and then aggregate to close an aperture in the test cartridge. The measure is expressed as the closure time and will be reported as normal or abnormal.

The testing strategy uses two reagent cartridges. First, a collagen/ epinephrine cartridge is used to screen for defects. If the first cartridge is abnormal a second cartridge, Collagen / ADP, is used to differentiate aspirin-like defects from other defects. The table below outlines the expected reporting patterns.

Note that abnormal findings have been reported on patients with hematocrits below 35% and with platelet counts below 150,000/ mm3. These findings are not necessarily artifacts of the testing system and may reflect the clinical condition.

For ordering, the test name in the Siemens system is Platelet Function, Qualitative and the Lab computer code is PFAQ.


© 2004 Medical Center of Louisiana
Page updated: 9/24/04