Use of Small Aliquots of Frozen Red Blood Cells as Controls for in Vitro P50 Measurements over Extended Periods.

Small aliquots of red cells with low, normal and high P50 values were frozen with 40 WV glycerol and stored at -80 C for at least 1 year. After thawing and washing, these red blood cells were used as controls for P50 measurements. In studies conducted over a 3-year period, this quality control system has been shown to be a convenient, stable and reproducible way to assess the instruments used for P50 measurements as well as the technicians conducting the tests.