How is the fludrocortisone suppression test performed in the workup of hyperaldosteronism?

Updated: Oct 19, 2018
  • Author: George P Chrousos, MD, FAAP, MACP, MACE, FRCP(London); Chief Editor: Robert P Hoffman, MD  more...
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Answer

The fludrocortisone suppression test uses fludrocortisone (0.1 mg every 6 h) and salt loading. [38, 39] Patients receive 0.1 mg oral fludrocortisone every 6 hours for 4 days, together with slow-release potassium chloride supplements (every 6 h at doses sufficient to keep plasma potassium close to 4 mmol/L). Serum potassium is measured four times daily. High-sodium diet plus sodium chloride tabs are administered (30 mmol 3 times daily with meals) to maintain a urinary sodium excretion rate of at least 3 mmol/kg body weight. On day 4, plasma cortisol is measured at 7 or 8 AM and 10 AM, and plasma aldosterone concentration and renin are measured at 10 AM, with the patient in the seated position.

Upright plasma aldosterone higher than 6 ng/dL on day 4 at 10 AM confirms PA, provided that PRA is suppressed to less than 1 ng/mL/h, plasma potassium levels are normal and 10 AM plasma cortisol concentration is lower than the value obtained at 7 AM (to exclude a confounding ACTH effect). The test should not be performed in patients with uncontrolled hypertension, congestive heart failure, or arrhythmias, whereas false negative results may be obtained in renal insufficiency.

The use of the combined fludrocortisone-dexamethasone suppression test (FDST), which involves the co-administration of dexamethasone 2 mg at midnight, has been recently applied by some investigators to eliminate the stimulatory input of ACTH on aldosterone secretion, thus increasing substantially the sensitivity and specificity of the FDST and enabling the detection of milder forms of primary hyperaldosteronism. [18, 32, 35, 34, 40, 41]


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