Normal hemoglobin-oxygen affinity

Hemoglobin-xoygen affinity is known to vary in a number of disease states. The authors measured the continuous affinity of blood from healthy subjects and, using mathematical data reduction techniques, calculated coefficients for rational function models of average normal affinity, plus or minus 2 standard deviations, and 95 per cent confidence limits. Average normal P50 was 27.10 torr, with a two-standard-deviation range of 25.85 to 28.35; P50s of the 95 per cent confidence limits were 26.69 and 27.53 torr. The affinity usually accepted as standard lay between or very near to the 95% confidence limits of normal throughout its range. It is concluded that the range of normal affinity is narrow and that, for most practical purposes, standard affinity adequately represents normal affinity. There should be little difficulty in distinguishing from normal the shifts that occur in certain disease conditions.