Diagnostic Use
Platelet function testing is used to evaluate platelet activity and diagnose bleeding disorders.It assesses how well platelets respond to activation and aggregation stimuli. The PFA-200 system provides a quantitative measure of platelet function in anticoagulated whole blood. It simulates the process of platelet adhesion and aggregation following vascular injury. The system uses cartridges with a membrane coated with collagen and either epinephrine or ADP. Blood is drawn through a capillary and aperture cut into the membrane at high shear stress, mimicking conditions in the normal circulation. Platelets adhere and aggregate at the aperture, building a stable platelet plug and finally arresting the blood flow. The analyser measures time to occlusion. This is reported as the closure time in seconds.
Clinical applications include: diagnosing platelet function disorders such as Glanzmann thrombasthenia or Bernard-Soulier syndrome; evaluating unexplained bleeding in patients with normal platelet counts, monitoring antiplatelet therapy (e.g., aspirin, clopidogrel) in cardiovascular disease and preoperative screening in patients with bleeding history or on antiplatelet drugs.
Interpretation
The collagen/epinephrine cartridge is used as the screening test. If this is normal then the platelet function is normal.
If the collagen/epinephrine cartridge is abnormal, the collagen/ADP cartridge is performed. The collagen/ADP cartridge is generally normal if the patient has taken aspirin or aspirin-containing drugs.
If both tests are abnormal it indicates either a very low platelet count or haematocrit or a non-Acetyl salicylic acid affected platelet function defect.
The PFA is affected by any drugs that alter platelet function including non-steroidal anti-inflammatories, ticlopidine, persantin and GPIIbIIIa inhibitors. Other substances such as garlic have been shown to prolong closure times.
Uncertainty of Measurement
Collagen/EPI: 22%, Collagen/ADP:15%