Introduction

Endogenous carboxyhemoglobin production is a byproduct of hemoglobin metabolism and is significantly increased in human patients with hemolytic anemia (HA). We aimed to investigate its diagnostic and prognostic utility in dogs with HA.

Methods

A prospective observational study. Comparisons between dogs with HA, non-hemolytic anemias (NHA) and healthy controls were performed using the Mann-Whitney and Kruskal-Wallis tests. Receiver-operator characteristic (ROC) analyses were used to examine the predictive utility of carboxyhemoglobin for the diagnosis of HA in anemic dogs, and for outcome prediction.

Results

Study groups included 24 dogs with HA (immune-mediated HA, n=18; splenic mass/torsion, n=5; Evans syndrome, n=1), 26 dogs with NHA (kidney disease, n=14; immune-mediated thrombocytopenia, n=6; miscellaneous, n=6) and 19 control dogs (including dogs presenting for elective orthopedic surgery and healthy blood donors). Median (IQR) carboxyhemoglobin (%) was 7.6 (2.375), 3.6 (1.075) and 3.6 (0.65) in the HA, NHA and control groups (P<0.001). Post hoc comparisons revealed significant differences between the HA group and either the NHA or control groups (P<0.001 for both) but not between the last two groups (P=0.89). Area under the ROC curve for carboxyhemoglobin as predictor of HA in anemic dogs was 0.99 (95% CI, 0.988–1.00), with an optimal cut-off point of >4.55% yielding sensitivity/specificity of 100%/92.31%, respectively. Carboxyhemoglobin levels were negatively correlated with the hematocrit (r_s=-0.58, P<0.001), but were not associated with outcome.

Conclusions

Carboxyhemoglobin proved an excellent biomarker of hemolysis in anemic dogs and might constitute a useful ancillary tool for diagnosing hemolytic anemias.