Platelet function analyzer

Associate Editors-in-Chief: Davide Capodanno, M.D. [mailto:Davide.Capodanno@jax.ufl.edu]

Overview
The Platelet Function Analyzer-100(PFA-100, Siemens Healthcare Diagnostics, Inc., Deerfield, IL) is a test based on the principle of shear-induced aggregation. Although it is not a COX-1specific assay, it allows monitoring of aspirin effects by providing a quantitative measure of platelet-related hemostasis in anticoagulated whole blood.

The system comprises a microprocessor-controlled tool and a disposable test cartridge containing a biologically active nitrocellulose membrane. To perform the test, 0.8 ml of citrated whole blood is transferred into the reservoir of the cartridge within 4 h of blood sampling. After warming the anticoagulated blood to 37 °C, the instrument aspirates a blood sample under vacuum from the reservoir through a 200 μm diameter stainless steel capillary and a 150 μm aperture cut into the membrane, which is coated with collagen and epinephrine (CEPI) or collagen and ADP (CADP).

The presence of these biochemical stimuli, and the high shear rates of 5000–6000 s−1 generated under the standardized flow conditions, result in platelet aggregate forms that block the aperture of the membrane. The time required to obtain full occlusion of the aperture is reported as the closure time (CT).

Prolonged CT with only the CEPI cartridge is observed with mild inherited platelet function disorders and with aspirin ingestion, while prolonged CTs with both CEPI and CADP cartridges are associated with more severe inherited platelet dysfunctions. An advantage of the PFA-100 application as a platelet function assay is that it is a rapid, accurate, simple, and reproducible test that requires only a small volume of blood. It cannot be considered as a point of care as minimal pipetting is required to use this test. One of its major disadvantages is that it is poorly sensitive in detecting effects of thienopyridines and therefore should not be used for this purpose. Newer generation assays are currently under development to assess thienopyridine effects.