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Objectives: To investigate the clinical significance of the pattern of Coombs’ test reactivity in dogs with immune-mediated haemolytic anaemia.

Methods: Sixty-five anaemic dogs with a positive Coombs’ test were included. Coombs’ testing was performed at 4 and 37°C with polyvalent canine Coombs’ reagent and antisera specific for each of canine immunoglobulin G, immunoglobulin M and complement factor C3. The impact of performing testing with only polyvalent antiserum at 37°C was assessed. Chi-squared tests were used to compare Coombs’ test reactivity in dogs with primary immune-mediated haemolytic anaemia (group A) and in dogs with concurrent/underlying disease (group B). Following Bonferroni correction, significance was set at P≤0·003.

Results: Eleven dogs would have been regarded as Coombs’ negative had they been tested with polyvalent antiserum at 37°C alone. Group A dogs were significantly more likely to be positive with polyvalent antiserum and/or anti-dog immunoglobulin G at 4 and/or 37°C (P≤0·001) and tended to be less likely to be positive with anti-dog immunoglobulin M at 4°C (P=0·040).

Clinical Significance: Testing of anaemic dogs with polyvalent Coombs’ reagent at 37°C was less sensitive than testing with monovalent reagents at 4 and 37°C. The pattern of Coombs’ test reactivity differed significantly between dogs with primary immune-mediated haemolytic anaemia and those with concurrent/underlying disease.