Red blood cell osmotic fragility confidence intervals: a definition by application of a mathematical model

The red blood cell osmotic fragility test is based on the measure of the re sistance of red blood cells to lysis as a function of decreasing NaCl conce ntration. Up to now, several methods have been used for recording these dat a, but for the first time, the human red blood cell osmotic fragility confi dence interval using the Orcutt mathematical model was determined. The abso rbance of the hemoglobin measured at 540 nm, released by the red blood cell s of 40 healthy adult individuals, was fitted to the equation Absorbance=p3 erfc ([NaCl] - p1/p2); p3 measures one half the absorbance produced by max imum red blood cell hemolysis, pi is the [NaCl] producing 50% red blood cel l hemolysis, and p2 is the dispersion in [NaCl] producing red blood cell he molysis. Confidence intervals (mean+/-SD) for the three parameters were as follows: p1=4.2718+/-0.1848; p2=0.1947+/-0.0391, and p3=0.5568+0.0426. The usefulness of this osmotic fragility data analysis method using two patholo gical samples (P-thalassemia minor and hereditary spherocytosis) was demons trated. Parameters of the fitted data were compared with those obtained by the conventional recording method of Beutler.