Use of erythrocyte fragility profiles for monitoring immune-mediated haemolysis in horses.

The fragility of erythrocytes is easily demonstrated by their ability to withstand osmotic swelling and lysis in solutions of increasingly hypotonic saline. In healthy animals a plot of percentage haemolysis against increasing hypotonicity produces a sigmoid curve. Using the same data a derivative curve calculated from haemolytic increments shows a normal distribution of fragility within samples. In enhanced fragility due to immune-mediated haemolytic anaemia, these profiles of haemolysis are markedly altered and the derivative curve becomes multiphasic, indicating the presence of subpopulations of erythrocytes with differing fragility ranges. Analysis of these profiles in a case of intravascular immune-mediated haemolysis in a horse provided useful graphic information for diagnosis and prognosis. In particular, the size of the subpopulation showing increased fragility could be assessed in the acute phase and monitored during recovery.