In vitro measurement of P50--the pH correction, and use of frozen red blood cells as controls.

The Unicam Spectrophotometer, the IL 282 CO-Oximeter, and the Hemoscan were used to measure the in vitro P50 using 1, 20--45, and 50% hematocrit values of red blood cells suspended in autologous plasma or phosphate buffered saline at pH of 6.7--7.7. The relation between pH and P50 was a linear correlation for washed red blood cells by all three methods whereas the relation between pH and P50 was a log correlation for red blood cells in plasma. Multiple units of red blood cells with low 2,3 diphosphoglycerate (2,3 DPG) and increased affinity for oxygen, with normal 2,3 DPG and normal affinity for oxygen, and above normal 2,3 DPG and decreased affinity for oxygen, were frozen in 10 ml aliquots with 40% w/v glycerol and maintained at -80 degrees C. One tube of each level of 2.3 DPG was thawed, washed, and suspended in buffer daily to yield P50 values of 17.5 +/- 0.67, 29.7 +/- 0.92, or 41.2 +/- 0.72 torr at pH 7.2 in order to have a control of both instrumentation and personnel.