Last reviewed: 4 Sep 2023
Last updated: 13 Jan 2021
Summary
Definition
History and exam
Key diagnostic factors
- absence of hypovolemia
- absence of hypervolemia
- absence of signs of adrenal insufficiency or hypothyroidism
- nausea
- vomiting
- altered mental status
- headache
- seizure
- coma
More key diagnostic factors
Other diagnostic factors
- no history of recent diuretic use
Other diagnostic factors
Risk factors
- age >50 years
- pulmonary conditions (e.g., pneumonia)
- nursing home residence
- postoperative state
- malignancy
- medication associated with SIADH induction
- central nervous system (CNS) disorder
- endurance exercise
More risk factors
Diagnostic investigations
1st investigations to order
- serum sodium
- serum osmolality
- serum BUN
- urine osmolality
- urine sodium
More 1st investigations to order
Investigations to consider
- diagnostic trial with normal saline infusion
- serum uric acid
- fractional excretion of sodium
- fractional excretion of urea
- serum TSH
- serum cortisol level
- serum arginine vasopressin (AVP)
More investigations to consider
Treatment algorithm
ACUTE
severe symptoms
mild to moderate symptoms
asymptomatic with sodium ≥125 mEq/L
ONGOING
persistence of chronic SIADH
Contributors
Authors
Megan Dixon, MD
Nephrologist
Arizona Kidney Disease and Hypertension Center
Phoenix
AZ
Disclosures
MD declares that she has no competing interests.
Howard Lien, MD, PhD
Professor Emeritus of Medicine
Division of Nephrology
University of Arizona
Tucson
AZ
Disclosures
HL is an author of a reference cited in this topic.
Peer reviewers
Judith H. Veis, MD
Associate Director
Nephrology
Washington Hospital Center
Washington
DC
Disclosures
JHV declares that she has no competing interests.
Laurie Solomon, MD, FRCP
Consultant Nephrologist
Renal Unit
Lancashire Teaching Hospitals
Fulwood
Preston
UK
Disclosures
LS declares that he has no competing interests.
Differentials
- Pseudohyponatremia
- Hypovolemia
- Cerebral salt-wasting
More DifferentialsGuidelines
- Clinical practice guideline on diagnosis and treatment of hyponatraemia
More GuidelinesLog in or subscribe to access all of BMJ Best Practice
Use of this content is subject to our disclaimer