In vitro pH effects on in vivo recovery and survival of platelets: an analysis by the BEST Collaborative

The pH environment of stored platelet (PLT) products is recognized as an important factor and is generally used as a key surrogate measure of PLT viability. It is the only in vitro measurement that has been translated into industry standards and regulatory rules or specifications for storage of PLT products. The objective of this study was to evaluate the effect of in vitro pH on the in vivo recovery and survival of autologous PLT products.

Data from individual autologous radiolabeled PLT kinetic studies were solicited from independent laboratories. PLTs stored for at least 5 days in 100 percent autologous plasma with a pH(22 degrees C) of at least 6.2 were analyzed. Data were fit to a mixed-effects regression model with fixed effects of pH(22 degrees C), time of storage, and preparation method-storage bag combination.

Eight research laboratories reported 476 individual recovery and survival results with associated pH before labeling from a variety of autologous, radiolabeled PLT kinetic studies from September 1999 to March 2005. These results are from 254 individual subjects who donated a total of 386 PLT units, with up to nine collections per subject reported. The effect of pH on either PLT recovery (p = 0.86) or survival (p = 0.55) was not significant. Time of storage and the method-bag combination both had significant effects on these outcomes (p < 0.0001).

These data suggest that there is no relationship between in vitro pH at a pH(22 degrees C) of at least 6.2 and in vivo PLT viability as measured by radiolabeled recovery and survival of autologous PLTs.