Evaluation of the oral fludrocortisone suppression test for diagnosing primary hyperaldosteronism in cats

Background: Primary hyperaldosteronism (PHA) in cats is suggested by clinical signs and an elevated plasma aldosterone- to-renin ratio (ARR), but a test to confirm the diagnosis is lacking. Hypothesis: Fludrocortisone does not suppress urinary aldosterone excretion in cats with PHA, but does so in cats with arterial hypertension because of other causes. Animals: Nineteen client-owned cats with arterial hypertension because of PHA (n = 9) or other causes (n = 10). Methods: Prospective clinical study. The urinary aldosterone-to-creatinine ratio (UACR) was determined in morning urine before, during, and after 4 days of oral fludrocortisone administration in a dose of 0.05 mg/kg q12h. Arterial blood pressure and plasma potassium concentration were measured before and after fludrocortisone administration. Results: A basal UACR above 46.5 9 10 9, the upper limit of the reference range, was found in 3 cats with PHA. All PHA cats had basal UACRs >7.5 9 10 9. In all non-PHA cats with a basal UACR >7.5 9 10 9, fludrocortisone administration induced >50% suppression. In contrast, fludrocortisone administration resulted in