Abstract
BACKGROUND: Heart failure-associated hypochloremia can be depletional from diuretics or dilutional from water retention. Serum osmolality reflects water balance but has not been evaluated in dogs with heart disease. HYPOTHESIS: To determine if serum osmolality is related to heart disease stage and amount of mathematical correction of serum chloride (Cl(-) ) concentrations in healthy dogs and dogs with myxomatous mitral valve degeneration (MMVD). ANIMALS: Seventy-seven dogs (20 healthy, 25 Stage B MMVD, 32 Stage C/D MMVD). METHODS: Serum Cl(-) concentrations were mathematically corrected. Osmolality was calculated (calOsm) and directly measured by freezing point depression (dmOsm) and compared by Bland-Altman analysis. Biochemical variables and osmolality were compared among healthy, Stage B, and Stage C/D dogs. Correlations were explored between osmolality and biochemical variables. Median and range are presented. P < .05 was considered significant. RESULTS: The calOsm was different among groups (P = .003), with Stage B (310 mOsm/kg; 306, 316) and C/D dogs (312 mOsm/kg; 308, 319) having higher calOsm than healthy dogs (305 mOsm/kg; 302, 308). Osmolality methods were moderately correlated (P < .0001, r(s) = .46) but with proportional bias and poor agreement. The amount of Cl(-) correction was negatively correlated with calOsm (P < .0001, r(s) = -.78) and dmOsm (P = .004, r(s) = -.33). Serum bicarbonate concentration was negatively correlated with Cl(-) (P < .0001, r(s) = -.67). CONCLUSIONS AND CLINICAL IMPORTANCE: Dogs with Stage B and Stage C/D heart disease had higher calOsm than healthy dogs. Osmolality was inversely related to the amount of Cl(-) correction, which supports its use in assessing relative body water content. Poor agreement between calOsm and dmOsm prevents methodological interchange.