Influence of mechanical trauma of blood and hemolysis on PFA-100 testing

Although the appropriate quality of samples is essential for platelet function testing, information is lacking on interference from mechanical trauma of blood and hemolysis on PFA-100 analyzer. Citrated blood collected from nine healthy volunteers was divided into three aliquots. The first aliquot ('A') was processed without further manipulation, whereas the second and third were subjected to mechanical trauma by two ('aliquot B') or four passages ('aliquot C') through a very fine needle (30 gauge) to produce hemolysis and cell trauma mimicking poor sample collection. Samples were tested on PFA-100 and Advia 2120, and plasma then separated and tested for lactate dehydrogenase (LDH) and hemolysis index. Negligible hemolysis was present in aliquot A (hemolysis index 0.2 ± 0.1, cell-free hemoglobin 0-0.5 g/l), whereas an increasing amount was present in aliquots B (hemolysis index of 13.1 ± 1.8, cell-free hemoglobin 6.0-6.5 g/l) and C (hemolysis index 24.0 ± 1.1, cell-free hemoglobin 11.5-12.0 g/l). Increases in LDH, and concomitant reductions in platelet and red blood cell counts were observed in aliquots B and C. In hemolyzed aliquots B, four out of nine samples yielded 'flow obstruction' with both PFA-100 agonist cartridges, whereas the closure times were dramatically prolonged in the remaining five samples. In hemolyzed aliquots C, flow obstruction was recorded in six of nine samples for collagen and ADP and all samples for collagen and epinephrine, whereas closure times of collagen and ADP in the remaining three samples were dramatically prolonged. Mechanical trauma of blood causing hemolysis makes PFA-100 testing unreliable. When flow obstructions are observed, the potential presence of hemolysis should be investigated.