Evaluation of Low Sodium:Potassium Ratios in Dogs

Sm Anim Clin Endocrinol 9[3]:20 Oct/Dec'99 Retrospective Study 0 Refs Editors: C.B. Chastain, DVM, MS, Dip ACVIM; D. Panciera, DVM, MS, Dip ACVIM; Carrie Walters, DVM, PhD, Dip ACVIM

Commentary on: L. Roth & R.D. Tyler; J Vet Diagn Invest 1999; 11:60-64

Clinical signs of primary hypoadrenocorticism are nonspecific. They vary from acute onset of severe weakness and depression to chronic, poorly defined illness. A sodium: potassium ratio less than 25 is frequently cited as highly suggestive of primary hypoadrenocorticism. However, there are other causes for low sodium: potassium ratios, including acute or end-stage chronic renal failure, urinary tract obstruction or rupture, and severe gastrointestinal disease.

Medical records of 37 dogs with a sodium: potassium ratio less than 24 were reviewed. Records on 34 were sufficiently complete to identify causes of the low sodium: potassium ratio. Primary hypoadrenocorticism was diagnosed in eight dogs based on clinical signs, clinical chemistries, and results of an adrenocorticotropic hormone (ACTH) stimulation test. Renal disease was present in 14 dogs. Decreased sodium:potassium ratio was also found in three dogs with disseminated neoplasia, two with pancreatitis, two with diabetic ketoacidosis, two with congestive heart failure, and one each with urinary bladder rupture, urinary bladder incarceration in a perineal hernia, concurrent Trichuris vulpis and Toxocara canis infection, pyometra, mushroom toxicity, and a behavioral disorder. Thoracic or abdominal effusion was present in four dogs with mammary adenocarcinoma, hemangiosarcoma, heart failure, or pancreatitis. The sodium: potassium ratio was between 20 and 24 in 22 dogs. Only two (13%) of these dogs had primary hypoadrenocorticism while nine had renal failure or urinary tract disease. Of eight dogs with a sodium:potassium ratio of 15-20, two had hypoadrenocorticism and four had renal or urinary tract disease. All four dogs with a sodium: potassium ratio less than 15 had primary hypoadrenocorticism. Serum potassium concentration was increased in all dogs in this study, while serum sodium was decreased in only 53%. The sodium:potassium ratio correlated closely with serum potassium concentration and less well with the serum sodium concentration. The authors concluded that renal or urinary tract disease is the most common cause of low sodium: potassium ratio and that sodium:potassium ratio less than 15 occurs most commonly in dogs with primary hypoadrenocorticism.

This study reiterates the importance of the ACTH stimulation test in establishing a diagnosis of primary hypoadrenocorticism. Because renal concentrating ability in dogs with primary hypoadrenocorticism may be impaired, it can be difficult to differentiate primary renal failure from primary hypoadrenocorticism. Because of the differences in prognosis and treatment, establishing a definitive diagnosis is essential in these cases. It is also important to note that not all dogs with primary hypoadrenocorticism have electrolyte abnormalities.

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