Quality control of platelets during storage by the PFA-100: a comparison to platelet aggregation

The PFA-100 examines platelet function by measuring closure time (CT) when whole blood is passing through a capillary and a filter membrane coated with a collagen/platelet agonist. Termination of the CT is achieved when adhered and aggregated platelets of the passing blood flow occlude the membrane. Two PFA-100 test cartridges are used to measure the CT of citrated whole blood; either the collagen/ADP (PCA) or the collagen/ epinephrine (PCE). We investigated the applicability of the PFA-100 test system for quality control of platelet concentrates in comparison with platelet aggregometry.

For platelet aggregation, the combination of ADP (100 microM/l) and collagen (20 microg/ml) were used as agonists (ADP/COL). In our test system, 25 microl epinephrine (10(-3) M) were added to the PCA cartridge (CT: PCAE) and 25 microl ADP (100 microM/l) to the PCE cartridge (CT: PCEA), respectively. Red blood cells from a blood group 0 donor were adjusted to a hematocrit of 43% using platelet rich plasma (8 x 10(5)/microl) of the respective platelet concentrate. Fourteen irradiated and non-irradiated platelet concentrates were examined on days 0, 3 and 5 after platelet preparation. Swirling without a scoring system and mean platelet volume (MPV) were also tested. Statistical analyses were performed by Pearson's range coefficient, the Mann and Whitney test, and the Wilcoxon test.

Swirling was seen in all platelet concentrates. Mean platelet volume was normal during the whole observation period like the PCAE in non-irradiated products. Only the PCAE showed finite CTs during the whole storage time. Consequently, further testing was performed exclusively with the PCAE. Weak but significant correlations could be found between the PCAE and ADP/COL (r = -0.53 for non-irradiated platelet products, r = -0.62 for irradiated platelet products, p < or = 0.0001). Platelet function significantly decreased to around 60% of the initial value in the PCAE on day 5 of storage, ADP/COL decreased to 35% of maximum amplitude. A further decrease of approximately 10% was observed in the irradiated products, a fact which was significant in the PCAE. Only in the irradiated platelet products did MPV show a weak but significant correlation with the PCAE (r = 0.45, p = 0.002).

Functional features of platelets from platelet concentrates characterized by ADP/COL induced aggregation can also be measured by the PFA-100. Yet, it has a higher sensitivity to platelet lesions induced by gamma-radiation. Further clinical studies will be necessary to determine whether PFA-measurements meet the quality criteria of MPV or swirling, or is superior in predicting in vivo viability. The relatively high cost of the test cartridge remains an obstacle for routine use.