Abstract
Decreased quantitative RPA of PRP is used to distinguish patients with von Wille-brand’s disease from normals and hemophiliacs. We observed that RPA (1.8 mg/ml final concentration) of PRP from 9 normals varied markedly with time after PRP preparation. In 6/9 the initial RPA was greatest and decreased progressively with time. In 3/9 RPA increased over the first half hour and then decreased progressively. The decrease from peak values was 37 ±12% (mean±1 SD) at 1 hr, 69 ±20% at 2 hr and 70±10% at 2.5 hr.Several data suggest a role for pH in this phenomenon: (1) pH of the PRP’s increased with time and the decreases in RPA paralleled the increases in pH (2) maintaining the PRP under a 5% CO2-95% O2 atmosphere prevented the rise in pH and lessened the decrease in RPA over time (3) rapidly increasing the pH to 8.3 by bubbling nitrogen through the PRP or titrating with base decreased RPA (81% and 55%) (4) immediate back titration restored the RPA.We conclude that quantitative RPA changes with time after PRP preparation and this is probably in part a function of pH. Since pH change with time is variable for different PRP preparations, choosing an arbitrary time limit after PRP preparation for performing studies is an inadequate control. Quantitative RPA should be pH controlled.
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