Erythrocyte osmotic fragility: micromethod based on resistive-particle counting

A new procedure has been developed to measure the osmotic fragility of human erythrocytes. It is based on the resistive-particle counter and the finding that lysed erythrocytes have a lower electrical resistance than intact cells after the current in the sensing orifice reaches a critical value. The most suitable test conditions involve a 19 mu orifice, a high current setting, and the simple use of size discriminators to exclude lysed cells from being counted. Since only 1 to 5 microliter of blood are needed per salt concentration, a complete fragility test can be carried out with less than 50 mu of blood. Results with the new procedure were comparable to the classic spectrophotometric one for normal blood, in clinical conditions of increased or decreased erythrocyt osmotic fragility, and for different anticoagulants. It has a specific advantage in that ratio counting makes accurate pipetting of blood unnecessary.