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The page below is a sample from the LabCE course Fundamentals of Hemostasis. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Basic Laboratory Tests of Hemostatic Function - Platelet Function Assay

A platelet function assay (PFA) is a screening test for the evaluation of platelets/primary hemostasis. Common clinical applications include the following:
  • Preoperative evaluation of platelet function
  • Determining the presence of drug-induced platelet dysfunction
  • Determining platelet functionality in high-risk pregnancy
  • Evaluation of patients with suspected inherited or acquired platelet disorders such as von Willebrand disease
  • Evaluation of a bleeding patient
A PFA instrument is able to differentiate between drug-induced platelet defects and other platelet defects.
PFA tests are superior to the bleeding time test. The bleeding time is often not reproducible and, in spite of attempts at standardization, remains prone to variations in test results between persons performing the test. It is also relatively insensitive to platelet function. The bleeding time cannot be used to identify patients who may have recently ingested aspirin or non-steroidal anti-inflammatory drugs or patients who may have a platelet defect attributable to these drugs.
The bleeding time is used to assess platelet function, but may be affected by platelet quantity.
NOTE: Aspirin, and some other drugs, may falsely prolong bleeding times. Patients must be asked about aspirin use, and be aspirin free for 7-10 days prior to testing, for valid results.