Incidence, Severity and Prognosis Associated with Hyponatremia in Dogs and Cats

Background: Hyponatremia is a common electrolyte abnormality in human patients and is associated with substantial morbidity and death. The incidence and importance of hyponatremia in dogs and cats has not been determined. Hypothesis/Objectives: To describe the incidence of and prognosis associated with hyponatremia in dogs and cats at a university teaching hospital. Animals: Of 16,691 dogs and 4,211 cats with measured blood or serum sodium concentration. Methods: Retrospective study. Medical records of animals with a blood or serum sodium concentration measured during a 60-month period were reviewed to determine the severity of hyponatremia and its associated fatality rate. Cases with moderate (11-15 mmol/L below the reference range) or severe hyponatremia (≥16 mmol/L below the reference range) were further reviewed. Results: Of 4,254 dogs (25.5%) and 2,081 cats (49.4%) were diagnosed with hyponatremia. Case fatality rates of dogs and cats with hyponatremia were 13.7% and 11.9%, respectively, compared to 4.4% and 4.5% with a normal blood or serum sodium concentration (P < 0.0001). The magnitude of hyponatremia was linearly associated with a higher case fatality rate (P < 0.0001). Hyponatremia was associated with a lower case fatality rate than hypernatremia in the same population. Among the animals with moderate or severe hyponatremia, 92.1% of dogs and 90.6% of cats presented with community-acquired hyponatremia, and 7.9% of dogs and 9.4% of cats developed hospital-acquired hyponatremia. Conclusions and clinical importance: Hyponatremia was found commonly in this population and was associated with increased case fatality rate. Presence and severity of hyponatremia might be useful as a prognostic indicator.