Evaluation of a Platelet Function Analyser (PFA-100) in patients with a bleeding tendency

To investigate pre-analytical variables and the diagnostic performance of the platelet function analyser (PFA-100), a new device to test primary haemostasis in vitro by simulating platelet adhesion and aggregation under high shear stress.

Venous whole citrated blood is aspirated through a capillary towards an aperture of a collagen coated membrane containing either adenosine diphosphate (ADP) or epinephrine (EPI). The time needed for occluding this aperture by plug formation is called closure time (CT) and was assessed in 70 healthy subjects and 43 patients with a suspected mild bleeding disorder.

The reference range for the PFA-100 was found to be 82-159 s for EPI-CT and 62.5-120.5 s for ADP-CT. Duplicate analyses revealed a mean coefficient of variations of 7.1% (EPI-CT) and 5.7% (ADP-CT). The EPI- and ADP-CT of blood samples collected in the evening were significantly longer (p = 0.002 and p = 0.004, respectively) than the CT of blood samples collected in the morning. Acetylsalicylic acid(100 mg, 300 mg or 500 mg) administered as a single dose or daily on 10 consecutive days resulted in a prolongation of the EPI-CT, whereas the ADP-CT was not affected. EPI-CT was more sensitive in detecting acetylsalicylic acid (ASA) ingestion than was the bleeding time (BT). Sensitivity and specificity of the PFA-100 to detect von Willebrand disease (vWD) were comparable to the results obtained with the BT.

The PFA-100 represents a simple and easy to use test for investigation of primary haemostasis. Limitations of the system are: special citrated whole blood has to be proceeded within 0.5 to 4 h after sampling, duplicate measurements are necessary, and the results differ between blood sampled in the morning or in the afternoon. The data indicate that the test is sensitive to ASA intake and vWD. Its use is preferable to BT determination, because it is less invasive and more sensitive to abnormalities of primary haemostasis.