• Azathioprine;
  • Prednisolone;
  • Prognosis;
  • Spherocytosis;
  • Therapy

Background: Canine idiopathic immune-mediated hemolytic anemia (IMHA) is associated with a high mortality, especially in the 1st 2 weeks after diagnosis despite treatment.

Objectives: To determine treatment outcome and identify prognostic variables in order to define areas of future research.

Animals: One hundred forty-nine dogs with hematocrit <30% and either a positive Coombs' test or spherocytosis and with no evidence of disease that can trigger IMHA were included.

Methods: Retrospective cohort study. All dogs were treated with prednisolone and azathioprine according to a standard protocol. Survival analysis was performed by the Kaplan-Meier method. Variables recorded at the time of diagnosis were tested as possible prognostic variables in a univariate and multivariate Cox proportional hazard model.

Results: The main predictors for mortality in dogs with idiopathic IMHA are the presence of increased plasma urea concentration, bands, thrombocytopenia, and petechiae at the time of diagnosis. The estimated Kaplan-Meier half-year survival was 72.6% (95% confidence interval [CI]: 64.9–81.3%). Mortality occurred mostly within the 1st 2 weeks. Cox proportional hazards analysis indicated that increased plasma urea concentration, icterus, and petechiae were the major independent predictors of mortality in the 1st 2 weeks. In most dogs that survived IMHA, a 3-month protocol of azathioprine with prednisolone maintained clinical remission. The estimated half-year survival for dogs that survived the 1st 2 weeks was 92.5% (95% CI: 86–99.3%).

Conclusions and Clinical Importance: If the dogs survived IMHA, a 3-month protocol of prednisolone and azathioprine was effective with regard to survival and clinical outcome. Future research should be directed at identifying whether thrombotic tendency in dogs with IMHA is the main contributor to the development of increased plasma urea concentration, icterus, thrombocytopenia, and petechiae.