Hypochloremia is negatively associated with outcomes in cats with stable congestive heart failure

Objective: To assess the association between serum chloride concentration (s[Cl-]) and survival outcomes in cats with stable congestive heart failure (CHF). Methods: This was a single-institution retrospective study. Medical record reviews of 178 client-owned cats from 2014 through 2024 identified 84 cats meeting inclusion criteria of stable CHF at least 1 week after hospitalization. Cats with significant gastrointestinal disease were excluded. Biochemical parameters, medications, and survival were analyzed using Kaplan-Meier methods. Forward stepwise Cox proportional hazards regression was used to identify independent predictors of death risk. Results: Hypochloremia was defined as s[Cl-] < 112 mEq/L (the lower limit of the reference range). Fifteen cats were hypochloremic, and 69 cats were normochloremic. Hypochloremia was independently associated with a higher risk of death (hazard ratio, 2.82), and survival was shorter for cats with s[Cl-] < 112 mEq/L (159 days) compared to cats with s[Cl-] > 112 mEq/L (392 days). Diuretic dose was significantly higher in the hypochloremic group but was not an independent predictor of outcome in multivariable modeling. Two other confounders independently predicted outcome in the multivariable model (higher death risk with pimobendan use; hazard ratio, 1.96; lower death risk with normal BUN < 28 mg/dL; hazard ratio, 0.45). Conclusions: In this cohort of cats with stable CHF, hypochloremia was independently associated with significantly shorter survival and increased mortality risk. Clinical Relevance: Efforts to normalize s[Cl-] in cats with CHF merit consideration.