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: n 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.