White blood cell count and the sodium to potassium ratio to screen for hypoadrenocorticism in dogs.

Background: Abnormal sodium to potassium (Na:K) ratios can raise suspicion for hypoadrenocorticism (HA). Although dogs with HA usually have normal leukograms, their white blood cell counts may be useful in screening for HA.

Objectives: To examine the utility of combining the Na:K ratio with white blood cell counts to screen for HA in hospitalized dogs requiring fluid treatment administered i.v..

Animals: Fifty-three dogs with confirmed HA and 110 sick dogs confirmed not to have HA.

Methods: Retrospective, case-control study. Dogs were included if they were hospitalized and administered fluids i.v., had a complete blood count and measurement of serum Na and K concentrations. HA was diagnosed using an ACTH stimulation test, or ruled out by measurement of basal serum cortisol concentration.

Results: The receiver operating characteristic (ROC) curve for the lymphocyte count was not significantly different from the ROC curve of the Na:K ratio (P = .55). The ROC curve for the model combining the Na:K ratio and lymphocyte count was superior for identifying dogs with HA compared to the Na:K ratio (P = .02) or lymphocyte count (P = .005) alone. At the 100% sensitivity cutoff, lymphocyte count was more specific for detection of HA than Na:K (P < .001).

Conclusions And Clinical Importance: A combination of the Na:K ratio and lymphocyte count provides a better screening test for HA compared to the Na:K ratio or lymphocyte count alone. At 100% sensitivity, the lymphocyte count is a more specific test for HA than the Na:K.