Osmotic fragility of erythrocytes in clinically normal dogs and dogs infected with parasites.

The osmotic fragility of the erythrocytes was measured in blood samples collected from randomly selected healthy and infected dogs at a dogs' rescue shelter. The dogs were classified into six groups on the basis of the final diagnoses from clinical, post mortem and laboratory findings. The minimum (less than 5 per cent) and maximum (more than 90 per cent) haemolysis of the erythrocytes of the clinically normal dogs (group 1), occurred in 0.60 per cent and 0.30 per cent solutions of sodium chloride (NaCl). For the non-anaemic hookworm-infected dogs (group 2a) the respective values were 0.8 per cent and 0.4 per cent NaCl, and for the anaemic hookworm-infected dogs (group 2b) they were 0.85 per cent and 0.5 per cent NaCl, respectively. The erythrocytes from dogs with Babesia canis (group 3), concurrent hookworm and B canis (group 4) and Ehrlichia canis infections (group 5) had minimum haemolysis in 0.75 per cent NaCl and maximum haemolysis at between 0.20 per cent and 0.35 per cent NaCl solutions. The derivative fragiligrams for groups 2a, 2b, 3 and 4 were shifted to the left, whereas the fragiligram for group 5 was similar to that for the clinically normal dogs (group 1). The left shift for the hookworm-infected dogs was due to the increased osmotic fragility of a minor sub-population of the erythrocytes, but for the dogs infected with B canis major sub-populations of the erythrocytes had an increased osmotic fragility.