Relapse Risk Factors for Immune-Mediated Hemolytic Anemia: A Retrospective Study of 163 Dogs

Immune-mediated hemolytic anemia (IMHA) is defined as an immune-mediated destruction of erythrocytes. Relapses are recognized, but risk factors are poorly defined. We hypothesized that a lower packed cell volume (PCV) on presentation, more transfusions during hospitalization, or a higher total bilirubin would be associated with an increased risk of relapse. IMHA was defined as a PCV less than 30% at diagnosis with two of the following identified: spherocytes, positive Coombs test, elevated total bilirubin, hemoglobinemia, or positive slide agglutination. This was a retrospective study evaluating 163 dogs between January 2005 and December 2019 from one specialty hospital. There were 13 relapses. The probability (95% confidence interval [CI]) of relapse by 3 and 12 mo was 0.05 (0.02-0.13) and 0.11 (0.06-0.22). The probability (95% CI) of relapse by 12 mo in patients who required two or more transfusions was 0.20 (0.09-0.42) compared with 0.07 (0.02-0.19) in patients who did not (P = .191). A lower PCV at diagnosis was not associated with an increased risk of relapse (hazard ratio [95% CI] 0.95 [0.86-1.04], P = .238). A higher total bilirubin was associated with a significantly increased risk of relapse (P = .003). With each increase of 1 mg/dL of total bilirubin, there was a 0.17 (95% CI 0.06-0.28) increase in the probability of relapse. These patients would likely need closer monitoring.