White Blood Cell Count and the Sodium to Potassium Ratio to Screen for Hypoadrenocorticism in Dogs

Abstract

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