Studies on the osmotic fragility of incubated normal and abnormal erythrocytes.

The osmotic fragility of erythrocytes is known to undergo alterations when whole blood is incubated under aseptic conditions for 24 hours. The osmotic fragility of spherocytes increases considerably ( 1 ). Normal erythrocytes undergo a slight increase in fragility (2) and by contrast the osmotic fragility of leptocytes and certain other erythrocytes (3) is decreased. The sequence of events associated with this divergent change and the factors which influence it are the subjects of this study. Under certain circumstances the normal erythrocyte may behave as an osmometer (4). Though not implying "rupture" of the erythrocyte (5), osmotic lysis occurs when the red cell volume increases to a critical value (6, 7). In in vitro systems, the degree of osmotic lysis which may occur is affected by pH, temperature, and tonicity (8) of the surrounding medium. If these variables are held constant, then alterations in the osmotic fragility of the incubated erythrocytes would reflect changes in their milieu interne which result from metabolic activity during incubation. Abnormality of shape or volume of erythrocytes or both is presumed to alter their osmotic fragility by virtue of altering the span between the initial volume and the critical hemolytic volume of the cell (6, 7, 9). However, abnormal cell geometry does not, by this means, account for the apparent paradoxical response of the osmotic fragility of leptocytes to incubation. If the initial direction of change in the osmotic fragility of incubated leptocytes were abnormal, an abnormality of erythrocyte metabolism would be suggested. If the initial change in osmotic fragility were normal but