Hyponatraemia

Last reviewed: 24 Apr 2022
Last updated: 27 Oct 2020

Summary

Definition

History and exam

Key diagnostic factors

  • presence of risk 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 mucous membranes
  • absence of axillary sweat
  • oedema
  • rales or crackles on lung auscultation
  • polyuria
More key diagnostic factors

Other diagnostic factors

  • history of hyperlipidaemia or paraproteinaemia
Other diagnostic factors

Risk factors

  • older age
  • hospitalisation
  • 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, urea, 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 adrenocorticotrophic 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

acute onset (<48 hours) and/or symptomatic

ONGOING

chronic onset (≥48 hours) or asymptomatic

overcorrection of serum sodium concentration

Contributors

Authors

Judith H. Veis, MD
Judith H. Veis

Associate Director

Nephrology

MedStar Washington Hospital Center

Washington

DC

Disclosures

JHV declares that she has no competing interests.

Peer reviewers

Gregor Lindner, MD

Director

Department of Internal & Emergency Medicine

Hirslanden Klinik Im Park

Zurich

Switzerland

Disclosures

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

Charleston

SC

Disclosures

MEU declares that he has no competing interests.

  • Hyponatraemia images
  • Differentials

    • Hypertonic hyponatraemia
    • Pseudohyponatraemia
    • Assessment of hyponatraemia
    More Differentials
  • Guidelines

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