Proficiency testing/external quality assurance for the PFA-100(®)

Platelet function testing is integral to haemostasis investigations and the Platelet Function Analyser-100 (PFA-100(®)) is globally the most utilised primary haemostasis-screening instrument. External Quality Assurance (EQA) (or proficiency testing) is critical to ensuring quality of test practice, but EQA for platelet function is logistically challenging and actual test-challenges generally not possible.

A novel approach was therefore developed whereby a range of formulated test tubes are distributed to EQA participants to which citrated normal whole blood collected on site is added, thereby creating test material that can be locally evaluated. Several exercises have been conducted over the past four years (total of 18 challenges, most designed to mimic an aspirin effect or a mild or severe primary haemostasis defect, tested in 26-47 laboratories).

Numerical results for PFA-100(®) closure times (CTs) and interpretive comments provided by participants were analysed. Reported CTs for each challenge were within limits of expectation and good reproducibility was evidenced by repeated challenges. Coefficients of variation (CVs) generated for two PFA-100(®) cartridge types (C/ADP and C/Epi) for challenges [median (range): 14.8 (3.9-29.5) and 13.9 (0.6-29.5)] was similar to those obtained using native whole blood [15.6 (14.2-18.9) and 17.3 (13.5-20.5)]. Interpretations were in general also consistent with expectations and test data provided by laboratories.

In conclusion, an EQA process for the PFA-100(®) has been developed that includes a highly reproducible test-challenge process, not only proving the concept is possible for platelet function testing, but also providing a valuable mechanism for monitoring and improving laboratory performance.