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Licensed Unlicensed Requires Authentication Published by De Gruyter November 12, 2020

Differentiating syndrome of inappropriate ADH, reset osmostat, cerebral/renal salt wasting using fractional urate excretion

Farahnak Assadi ORCID logo and Mojgan Mazaheri ORCID logo



Clinical and laboratory data of reset osmostat (RO) and cerebral/renal salt wasting (C/RSW) mimic syndrome of inappropriate antidiuretic hormone (SIADH) and can pose diagnostic challenges because of significant overlapping between clinical and laboratory findings. Failure to correctly diagnose hyponatremia may result in increased mortality risk, longer hospital stay, and is cost-effective. We aim to illustrate clinical and laboratory similarities and difference among patients with hyponatremic disorders and discuss the diagnostic value of factional uprate excretion (FEurate) to differentiate SIADH from RO and C/RSW.

Case presentations

We report the use of FEurate in the evaluation of three patients with hyponatremia and elevated urine osmolality in the absence of edema or clinical evidence of dehydration to differentiate SIADH from RO and C/RSW.


Measurement of FEurate may offset in part the diagnostic confusion imparted by the diagnoses of SIADH, RO, and C/RSW.

Corresponding author: Farahnak Assadi, MD, Department of Pediatrics, Division of Nephrology, Rush University Medical Center, 445 East North Water Street, Suite 1804, Chicago, IL, USA, Tel: 312 560 0477, Fax: +888 757 4314, E-mail:

  1. Research funding: None declared.

  2. Author contributions: All authors contributed equally in the study design; in the collection, analysis, and interpretation of data; in the writing of the report; or in the decision to submit the report for publication.

  3. Competing interests: The authors declare that they have no relevant financial interests.

  4. Ethical standard: The manuscript does not contain experimental or interventional study.


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Received: 2020-06-24
Revised: 2020-08-28
Accepted: 2020-08-31
Published Online: 2020-11-12
Published in Print: 2021-01-27

© 2020 Walter de Gruyter GmbH, Berlin/Boston

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