Beginning September 15, 2000 the Hemostasis Laboratory will offer the Platelet Function Test utilizing a new Platelet Function Analyzer, the PFA-100TM. This test will replace the Bleeding time as the primary test for evaluation of platelet dysfunction. Platelet function testing by PFA can be ordered without approval. A bleeding time will now require approval by the Hematology staff at all times.
The PFA-100 analyzer and test cartridge system simulate the in-vivo hemodynamic conditions of platelet adhesion and aggregation following vascular injury, allowing for rapid and meaningful evaluation of platelet function on citrate anticoagulated blood. This test has been shown in the recent literature to be a reliable test for detection of platelet dysfunction due to drugs, decreased von Willebrand factor and other thrombocytopathies.
The principle of the PFA is very elegant. Citrated blood is forced through a capillary system to a membrane with a central aperture coated with collagen and either epinephrine or ADP. The time required to obtain full occlusion of the aperture by a platelet plug is the closure time and is reported in seconds. The blood specimen will first be screened with the collagen/epinephrine cartridge which is highly sensitive in detecting all platelet dysfunction states. If this initial test is abnormal then the blood will be tested with the collagen/ADP cartridge. If this latter test is normal, the findings are indicative of a probable drug effect. If both tests are abnormal further testing should be done to determine the cause of the platelet defect.
Factors that can give a prolonged closure time are similar to those that prolong the Bleeding time and include: