Effects of extended storage of blood samples on the results of platelet function testing: an in vitro stability study

In the present study, we aimed to explore the effects of extended storage of blood samples from 30 patients on the results of platelet function testing using the PFA-200 device (Collagen/EPI and Collagen/ADP tests), Multiplate instrument (ASPI, ADP, and TRAP tests), and VerifyNow analyzer (Aspirin and PRU tests). We determined platelet function (1) immediately after blood collection (baseline), (2) after storage of blood samples at room temperature for 3-4 h (i.e. the maximum sample storage period permitted by the manufacturers), and (3) after storage of blood samples for 5 h at room temperature (extended storage). Per the concept of acceptable change limits, platelet function was considered stable in time course if the median relative deviation from baseline values at a given time was <19% or <28%, depending on the test used. By applying our analyte stability limits, we found that blood samples could be stored for up to 5 h when performing the Collagen/ADP, ASPI, ADP, TRAP, Aspirin, and PRU tests. However, we observed significant deviations in the Collagen/EPI test results over time. The PFA-200 Collagen/EPI test results showed a median percentage deviation of 35% after 5 h of storage. However, no significant differences were observed between the measurements taken after 4 and 5 h of storage. We assume, that the baseline values of the Collagen/EPI test are measured incorrectly (presumably owing to malfunction of the test cartridges) and the following results are measured correctly.