Relationships between glucose, sodium and effective osmolality in diabetic dogs and cats

Objective: To examine the relative contributions of sodium and glucose to serum effective osmolality and the presence of abnormalities of sodium and osmolality in diabetic dogs and cats. Design: Retrospective study. Setting: A university‐based referral hospital. Animals: Diabetic dogs (n=14) and cats (n=13) consecutively admitted to the hospital over a 6‐month period. Interventions: None Measurements: Serum biochemistry assessments. Main results: The mean glucose concentration was higher in diabetic dogs than in diabetic cats. Total osmolality (Osm_T), effective osmolality (Osm_E), and the concentrations of sodium, potassium, blood urea notrogen, bicarbonate, and creatinine did not differ between species. Sodium abnormalities and hyperosmolality affected 44% and 81%, respectively, of the study group. However, marked hyperosmolality (Osm_E>330 mOsm/L) was found in only 33% of the study group. Serum sodium correlated closely with Osm_E in dogs and cats but serum glucose did not correlate with the Osm_E in either species. Subsets of dogs (n=10) and cats (n=7) with diabetic ketosis (DK) were examined separately. DK dogs had significantly lower sodium concentrations than DK cats and the proportion of DK dogs with hyponatremia was nearly 3 times greater than DK cats. Severe hyperosmolality (Osm_E>330 mOsm/L) was more common in DK cats than DK dogs. Conclusions: In diabetic dogs and cats, sodium, not glucose, was correlated with serum Osm_E and marked elevation in pretreatment Osm_E is uncommon. Compensatory reduction in serum sodium may be 1 mechanism for blunting changes in Osm_E in the presence of marked hyperglycemia.