In vitro changes in blood P50 and erythrocyte 2,3-diphosphoglycerate concentration

We studied in vitro changes in P50 and erythrocyte 2,3-diphosphoglycerate concentration occurring in blood 2 to 8 h after venipuncture. When blood was incubated at 37 degrees C, significant decreases in P50 were observed at 2, 4, and 8 hr. Such a change was significantly less when blood was kept at 4 degrees C. The rate of decrease in P50 was not changed when pH was altered by adding either lactic acid or sodium bicarbonate to the blood before incubation at 37 degrees C for 2 h. The erythrocyte 2,3-diphosphoglycerate concentration of blood incubated at 37 degrees C did not change by 2 h, but had significantly decreased by 4 h. To avoid in vitro changes, we recommend that P50 be determined as soon as possible for blood sampling.