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January 1985

Fractional Excretion of Sodium: Exceptions to Its Diagnostic Value

Author Affiliations

From the Department of Medicine, New England Deaconess Hospital (Dr Zarich), and the Renal Unit, Massachusetts General Hospital (Drs Fang and Diamond), Boston. Dr Diamond is now with the Department of Pathology, Harvard Medical School, Boston.

Arch Intern Med. 1985;145(1):108-112. doi:10.1001/archinte.1985.00360010144022

• Determining the cause of acutely deteriorating renal function is a common problem in clinical nephrology. The fractional excretion of filtered sodium (FENa) has been demonstrated to be a reliably discriminating test between prerenal azotemia and acute tubular necrosis. However, with increasing clinical use of the FENa, numerous reports of low FENa (<1%) have appeared. The clinical settings of these reports include oliguric and nonoliguric acute tubular necrosis, urinary tract obstruction, acute glomerulonephritis, hepatorenal syndrome, renal allograft rejection, sepsis, and drug-related alterations in renal hemodynamics. One particular urinary index cannot be expected to reliably discriminate between prerenal azotemia and acute renal failure in all cases. The utility of the FENa test in the differential diagnosis of acute renal failure must be interpreted in conjunction with the patient's clinical course and the use of additional urinary and serum tests.

(Arch Intern Med 1985;145:108-112)