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Last reviewed: 4 Sep 2023
Last updated: 27 Oct 2020



History and exam

Key diagnostic factors

  • high fluid intake
  • fluid losses
  • history of diabetes mellitus
  • history of cirrhosis, nephrosis, congestive heart failure
  • nausea/vomiting
  • mild cognitive symptoms
  • altered mental status, seizures, coma
  • low urine output
  • weight changes
  • orthostatic hypotension
  • abnormal jugular venous pressure
  • poor skin turgor
  • dry mucus membranes
  • absence of axillary sweat
  • edema
  • rales or crackles on lung auscultation
  • polyuria
More key diagnostic factors

Other diagnostic factors

  • history of hyperlipidemia or paraproteinemia
Other diagnostic factors

Risk factors

  • older age
  • hospitalization
  • selective serotonin-reuptake inhibitor (SSRI) use
  • thiazide diuretic use
  • underlying medical conditions
  • use of other medications
  • MDMA (ecstasy) use
More risk factors

Diagnostic investigations

1st investigations to order

  • serum sodium concentration
  • serum electrolytes, BUN, creatinine, and glucose
  • serum osmolality
  • urine sodium concentration
  • urine osmolality
  • urine electrolytes
  • urine flow rate
  • electrolyte-free water excretion
  • fractional excretion of sodium
  • thyroid-stimulating hormone
  • serum cortisol level and/or adrenocorticotropic hormone test
  • serum lipids and serum protein electrophoresis
More 1st investigations to order

Investigations to consider

  • CT brain, chest, abdomen/pelvis
  • other tests targeted at evaluating the underlying cause
More investigations to consider

Treatment algorithm


acute onset (<48 hours) and/or symptomatic


chronic onset (≥48 hours) or asymptomatic

overcorrection of serum sodium concentration



Judith H. Veis, MD
Judith H. Veis

Associate Director


MedStar Washington Hospital Center




JHV declares that she has no competing interests.

Peer reviewers

Gregor Lindner, MD


Department of Internal & Emergency Medicine

Hirslanden Klinik Im Park




GL is an author of a number of references cited in this topic.

Michael E. Ullian, MD

Professor of Medicine

Division of Nephrology

Department of Medicine

Medical University of South Carolina




MEU declares that he has no competing interests.

  • Hyponatremia images
  • Differentials

    • Hypertonic hyponatremia
    • Pseudohyponatremia
    • Evaluation of hyponatremia
    More Differentials
  • Guidelines

    • Emergency management of severe symptomatic hyponatraemia in adult patients
    • Emergency management of severe symptomatic hyponatraemia in adult patients
    More Guidelines
  • Patient leaflets


    More Patient leaflets
  • Calculators

    Osmolality Estimator (serum)

    Fractional Excretion of Sodium

    More Calculators
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