Evaluation of urine electrolytes for the diagnosis of hypoadrenocorticism in dogs

Background Most dogs with primary hypoadrenocorticism (HA) have a mineralocorticoid deficiency, which decreases renal tubular sodium reabsorption and potassium excretion. Limited information is available concerning the clinical value of measuring urine electrolytes to aid in an HA diagnosis. Objectives We aimed to evaluate the diagnostic utility of urine electrolyte measurements in dogs with HA. Methods Urine sodium and potassium concentrations were measured in 89 dogs, including 39 dogs with HA and 50 controls with nonadrenal illness. Fractional excretions of sodium (FENa) and potassium (FEK) were also calculated. Urine electrolytes and fractional excretion values were compared between the groups. Sensitivities and specificities were determined for various cut-points. Results The median urine sodium to potassium (Na:K) ratio was twofold greater (P < .001), and median FENa was fourfold greater (P < .001) in HA dogs as compared with controls. However, no cut-point for any variable with >90% sensitivity or specificity provided a corresponding specificity or sensitivity of >50%. When only dogs with abnormal serum or plasma electrolytes were included in the analyses, absolute urine electrolyte concentrations and FENa were not different between study populations (P > .05 for all comparisons), but the FEK was increased (P = .005) and the urine potassium:creatinine ratio was decreased (P < .001) in the control dogs compared with the dogs with HA. Conclusions Urine electrolyte concentrations and fractional excretions are altered in dogs with HA. However, substantial overlap exists with control dogs with nonadrenal illness. Therefore, these values are unlikely to have diagnostic utility for dogs with HA.