A theoretical approach of the measurement of osmotic fragility of erythrocytes by optical transmission

The osmotic fragility of the erythrocyte membrane to hypotonic solutions is investigated theoretically. The fragility curves exhibit a strong transmit tance rise. This variation is assumed to result from changes in the scatter ing properties of erythrocytes under dialysis resulting from swelling and h emolysis. The refractive indices of erythrocytes are obtained through the L orentz-Lorenz relation based on hemoglobin and water contents. The scatteri ng cross sections (needed to calculate the collimated transmittance) and th e forward scattered intensity (needed to calculate the incoherent transmitt ance) are expressed according to the simple algebraic relations of the anom alous diffraction approximation. It is shown that swelling (or shrinking) h as no influence on the collimated transmittance. Hemolysis alone causes the abrupt sigmoidal increase of the collimated transmittance with time. The p ossible transmittance increase (decrease) observed during swelling (shrinki ng) is due to incoherent transmittance and depends on the detecting solid a ngle value of the experimental setup.