Validation of a test of the red cell membrane osmotic resistance

The aim of the present work was to validate a new technique for the measure ment of resistance of the red blood cell membrane using an automated appara tus called a Fragilimeter. Its principle lies in the measurement of the ext inction of a laser beam projected through a red blood cell suspension subje cted, by diffusion, to a variation of salinity from an isotonic equilibrium (154 mM NaCl) to, a hypotonic one, 25 mM NaCl. The variation of osmotic pr essure induces on the cells a progressive lysis and a modification of the e xtinction of the transmitted light. The validation of the method was based on the comparison between results obtained with the Fragilimeter and those obtained using the reference DACIE technique. Analyses were based on blood samples from healthy donors. The determination of the initial, the 50% and the full haemolysis thresholds allowed observation of the fragility of the cell, through its membrane resistance. The physical phenomenon measured in these cells when subjected to various ionic strengths is discussed on the b asis of observations realised by means of an optical microscope.