The normal range of osmotic fragility of red blood cells

With the technique of Parpart et al (1947), the normal range for osmotic fragility of red blood cells had been estimated to include 5%--45% haemolysis at a salt concentration corresponding to 4.5 g NaCl/l (Dacie 1954). This estimate may be questioned, however. Thus, nearly 20% of the data obtained from 50 presumably healthy subjects fell outside these limits. Furthermore, the distribution pattern was very asymmetric with erroneously small standard deviation. On the other had, if the technical conditions (salt concentration, buffer) were properly adjusted, nearly all the observations were located with the straight part of the s-shaped haemolysis curve and scattered symmetrically around the mean. Under these conditions, the normal range (mean +/- 2 SD) included 22%--88% haemolysis. Moreover, this wider range included about 95% of the observations, even adapted to the original experimental situation. The present estimates should therefore replace earlier statements in the literature.