Noninvasive pH measurement to monitor changes during suboptimal storage of platelet concentrates

Noninvasive pH measurement of platelet concentrates (PCs) was evaluated as a tool for the quality control of PC storage by simulating worst-case conditions.

PCs from pooling four buffy coats in 70% PAS-3M were both stored in bags wrapped to impair gas permeability and agitated or not until Day 9 of storage. pH values measured both in samples (electrode, blood gas analyzer) and noninvasively by fluorimetry (BCSI pH1000, Blood Cell Storage, Inc.) were compared groupwise and to changes in platelet (PLT) size and biochemical variables.

The noninvasive pH measurements agreed well with the results from each of the two reference methods (R(2) >0.9) in a wide range of pH values between 6.4 and 7.5. Changes of the pH of PCs (n=64) by all interventions (agitation or resting plus occlusion by 0, 25, 50, or 100%; n=8/group) were subtle but already significant after 20 to 24 hours of treatment in comparison to the controls. A steady state after Day 6 and reductions up to a mean pH of approximately 6.5 were observed. The extent of manipulation determined both the absolute pH differences to the controls and the interindividual variation of pH changes. Termination of the agitation significantly enhanced pH reduction by surface blockade. Significant changes were also observed for the mean PLT volume, β-thromboglobulin, and soluble P-selectin.

Noninvasive pH measurement in PCs using this technique reliably detects pH changes of 0.1 or more. Storage of PLTs in buffered additive solution requires profound impairment of gas exchange to trigger a substantial decline in pH.