Syndrome of inappropriate antidiuretic hormone

Overview 
Theory 
Diagnosis 
Management 
Follow up 
Resources 

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Última revisão: 15 Sep 2025

Última atualização: 25 Mar 2025

Syndrome of inappropriate antidiuretic hormone (SIADH) is defined as euvolemic, hypotonic hyponatremia secondary to impaired free water excretion, usually from excessive arginine vasopressin (AVP) release.

Severe neurologic symptoms, such as altered mental status, seizure, and coma, may result from SIADH and these are always treated with hypertonic saline, with close monitoring to avoid overcorrection of serum sodium.

Central pontine myelinolysis (osmotic demyelination syndrome) may occur with rapid correction of serum sodium in excess of 12 mEq/L/day.

Vasopressin receptor antagonists (also known as vaptans) are a class of medications that compete with the antidiuretic hormone AVP for binding at the vasopressin receptor, permitting free water excretion.

Definição

The syndrome of inappropriate antidiuretic hormone (SIADH) is characterized by hypotonic hyponatremia, concentrated urine, and a euvolemic state. The impairment of free water excretion is caused by increased arginine vasopressin (antidiuretic hormone or AVP) release. Pseudohyponatremia due to hyperglycemia, hyperlipidemia, or hyperproteinemia should be ruled out first. Renal failure, adrenal insufficiency, and appropriate release of AVP secondary to extracellular volume depletion (hypovolemia, due to gastrointestinal or renal loss) or intravascular volume depletion (hypervolemia due to congestive heart failure, cirrhosis of the liver, or nephrotic syndrome) must be ruled out in order to diagnose SIADH.

História e exame físico

Principais fatores diagnósticos

absence of hypovolemia
absence of hypervolemia
absence of signs of adrenal insufficiency or hypothyroidism
nausea
vomiting
altered mental status
headache
seizure
coma

Detalhes completos

Outros fatores diagnósticos

no history of recent diuretic use

Detalhes completos

Fatores de risco

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

Detalhes completos

Investigações diagnósticas

Primeiras investigações a serem solicitadas

serum sodium
serum osmolality
serum BUN
urine osmolality
urine sodium

Detalhes completos

Investigações a serem consideradas

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)

Detalhes completos

Algoritmo de tratamento

AGUDA

severe symptoms

mild to moderate symptoms

asymptomatic with sodium ≥125 mEq/L

CONTÍNUA

persistence of chronic SIADH

Colaboradores

Autores

Megan Dixon, MD

Nephrologist

Arizona Kidney Disease and Hypertension Center

Phoenix

Declarações

MD declares that she has no competing interests.

Yeonghau Howard Lien, MD, PhD

Professor Emeritus of Medicine

Division of Nephrology

University of Arizona

Tucson

Declarações

YHL is an author of a reference cited in this topic.

Revisores

Maryam Gondal, MD

Assistant Professor

Nephrology

Yale University

New Haven

Disclosures

MG declares that she has no competing interests.

Judith H. Veis, MD

Associate Director

Nephrology

Washington Hospital Center

Washington

Disclosures

JHV declares that she has no competing interests.

Laurie Solomon, MD, FRCP

Consultant Nephrologist

Renal Unit

Lancashire Teaching Hospitals

Fulwood

Preston

Disclosures

LS declares that he has no competing interests.

Peer reviewer acknowledgements

BMJ Best Practice topics are updated on a rolling basis in line with developments in evidence and guidance. The peer reviewers listed here have reviewed the content at least once during the history of the topic.

Disclosures

Peer reviewer affiliations and disclosures pertain to the time of the review.

References

Our in-house evidence and editorial teams collaborate with international expert contributors and peer reviewers to ensure that we provide access to the most clinically relevant information possible.

Key articles

Gross P. Clinical management of SIADH. Ther Adv Endocrinol Metab. 2012 Apr;3(2):61-73.Full text Abstract

Spasovski G, Vanholder R, Allolio B, et al. Clinical practice guideline on diagnosis and treatment of hyponatraemia. Eur J Endocrinol. 2014 Mar;170(3):G1-47.Full text Abstract

Ball S, Barth J, Levy M, et al. Society for Endocrinology endocrine emergency guidance: emergency management of severe symptomatic hyponatraemia in adult patients. Endocr Connect. 2016 Sep;5(5):G4-6.Full text Abstract

Verbalis JG, Goldsmith SR, Greenberg A, et al. Diagnosis, evaluation, and treatment of hyponatremia: expert panel recommendations. Am J Med. 2013 Oct;126(10 suppl 1):S1-42.Full text Abstract

Ellison DH, Berl T. The syndrome of inappropriate antidiuresis. N Engl J Med. 2007 May 17;356(20):2064-72.

Reference articles

A full list of sources referenced in this topic is available to users with access to all of BMJ Best Practice.

Differentials
- Pseudohyponatremia
- Hypovolemia
- Cerebral salt-wasting
More Differentials
Guidelines
- Emergency management of severe symptomatic hyponatraemia in adult patients
- Clinical practice guideline on diagnosis and treatment of hyponatraemia
More Guidelines
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Syndrome of inappropriate antidiuretic hormone

Resumo

Definição

História e exame físico

Principais fatores diagnósticos

Outros fatores diagnósticos

Fatores de risco

Investigações diagnósticas

Primeiras investigações a serem solicitadas

Investigações a serem consideradas

Algoritmo de tratamento

severe symptoms

mild to moderate symptoms

asymptomatic with sodium ≥125 mEq/L

persistence of chronic SIADH

Colaboradores

Autores

Megan Dixon, MD

Declarações

Yeonghau Howard Lien, MD, PhD

Declarações

Revisores

Maryam Gondal, MD

Disclosures

Judith H. Veis, MD

Disclosures

Laurie Solomon, MD, FRCP

Disclosures

Peer reviewer acknowledgements

Disclosures

References

Key articles

Reference articles

A full list of sources referenced in this topic is available to users with access to all of BMJ Best Practice.

Differentials

Guidelines

Log in or subscribe to access all of BMJ Best Practice

Log in or subscribe to access all of BMJ Best Practice

Log in to access all of BMJ Best Practice