How is a saline infusion test performed in the workup of hyperaldosteronism?

Updated: Sep 08, 2020
  • Author: George P Chrousos, MD, FAAP, MACP, MACE, FRCP(London); Chief Editor: Robert P Hoffman, MD  more...
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Patients stay in the recumbent position for at least 1 hour before and during the infusion of 2 liters of 0.9% saline intravenously (IV) over 4 hours, starting at 8:00–9.30 AM. Blood samples for renin, aldosterone, cortisol, and plasma potassium are measured at time 0 and after 4 hours, with blood BP and heart rate monitored throughout the test. Postinfusion plasma aldosterone levels less than 5 ng/dL make the diagnosis of PA unlikely. In individuals without primary hyperaldosteronism, plasma aldosterone levels should fall to less than 10 ng/dL. Plasma aldosterone values higher than 10 ng/dL confirm primary hyperaldosteronism, and levels 5-10 ng/dL may be considered borderline.

Cortisol levels are taken to exclude an adrenocorticotropic hormone (ACTH)–mediated rise in aldosterone. The modified saline infusion test, performed after dexamethasone administration (0.5 mg every 6 h for 2 consecutive days) to eliminate any ACTH effect on aldosterone secretion, has been shown to have higher sensitivity compared with the classic saline infusion test in one study. [38] Consider the risks of fluid expansion or hypokalemia in susceptible patients.

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