Suspected SIADH
Euvolemic hyponatremia with inappropriate urine concentration
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EndocrinologyManagement
SIADH Diagnosis and Management
SIADH Diagnosis and Management: Suspected SIADH → SIADH Diagnostic Criteria → Rule Out Other Causes → Identify Underlying Cause → Assess Severity.
Pathway Overview
14 steps
Algorithm Steps
14 total
01Start 02Action SIADH Diagnostic Criteria
All criteria required for diagnosis
- 1. Serum osmolality <275 mOsm/kg (hypotonic)
- 2. Urine osmolality >100 mOsm/kg (inappropriately concentrated)
- 3. Urine sodium >30 mmol/L (on normal salt intake)
- 4. Clinical euvolemia (no edema, no dehydration)
- 5. Normal thyroid and adrenal function
- 6. No recent diuretic use
03Decision Rule Out Other Causes
SIADH is diagnosis of exclusion
- Hypothyroidism: Check TSH
- Adrenal insufficiency: Check cortisol/ACTH
- Renal failure: Check creatinine
- Psychogenic polydipsia: Urine osmolality <100
- Diuretic use: Recent thiazide/loop diuretics
04Action Identify Underlying Cause
Common SIADH etiologies
- Malignancy: SCLC, head/neck, GI cancers
- CNS: Stroke, SAH, meningitis, trauma, tumor
- Pulmonary: Pneumonia, TB, COPD, positive pressure ventilation
- Medications: SSRIs, carbamazepine, NSAIDs, cyclophosphamide
- Post-surgical: Especially after pituitary surgery
- Idiopathic (elderly)
05Decision Assess Severity
Guide treatment urgency
- SEVERE symptoms: Seizures, coma, respiratory distress → Emergency treatment
- MODERATE symptoms: Confusion, nausea, headache → Prompt treatment
- MILD/Asymptomatic: Focus on underlying cause + gradual correction
06Action SEVERE Symptoms
Emergency treatment with 3% saline
- 3% Hypertonic saline 150 mL IV over 20 min
- Repeat up to 3 times in first hour if needed
- Target: 5 mmol/L rise in first 1-2 hours
- Max 10-12 mmol/L in 24h (avoid ODS)
- Transfer to ICU
07Action 1. Fluid Restriction
First-line for mild-moderate SIADH
- Restrict to 1000-1500 mL/day (or 500 mL below urine output)
- More restrictive if urine:serum osmolality ratio >1
- Include ALL fluids (oral + IV)
- Expected Na rise: 1-2 mmol/L/day
- Compliance is often challenging
08Action 3. Vasopressin Receptor Antagonists (Vaptans)
For refractory SIADH
- Tolvaptan: 15-60 mg PO daily
- Initiate in hospital (overcorrection risk)
- Do NOT use with hypertonic saline
- Monitor Na q6h for first 24-48h
- FDA: Avoid >30 days due to liver injury risk
- Conivaptan: 20 mg IV then 20-40 mg/day (short-term only)
09Warning ⚠️ Vaptan Precautions
Important safety considerations
- Contraindicated in hypovolemic hyponatremia
- Risk of rapid overcorrection → ODS
- Hepatotoxicity with prolonged use (tolvaptan)
- Must initiate in monitored setting
- Do not combine with 3% saline
10Action 4. Treat Underlying Cause
Essential for long-term management
- Discontinue offending medications
- Treat infection (pneumonia, CNS infection)
- Cancer treatment if malignancy-related
- Manage CNS pathology
- SIADH often resolves when cause addressed
11Action 5. Monitoring
Ongoing assessment
- Serum Na: q4-6h during active treatment
- Urine osmolality and output
- Fluid intake (strict I/O)
- Neurological status
- Max correction: 10-12 mmol/L in 24h
12Outcome SIADH Resolved/Controlled
Na normalized, underlying cause treated
13Warning Chronic SIADH
Long-term management needed
- Continued fluid restriction
- Salt tablets ± loop diuretic
- Consider vaptans PRN
- Regular Na monitoring
- Path rejoins step 07Shared downstream outcome
14Action 2. Adjunct Therapies
If fluid restriction insufficient
- Salt tablets: 3-9 g NaCl/day (with loop diuretic)
- Urea: 15-60 g/day (osmotic diuresis)
- Loop diuretic + salt: Furosemide + NaCl tablets
- Demeclocycline: 300-600 mg BID (induces nephrogenic DI)
- Path rejoins step 08Shared downstream outcome
Guideline Source
ESE/ESICM/ERA-EDTA Clinical Practice Guideline on Hyponatraemia + SIADH Expert Consensus
Clinical Safety Information
Clinical Decision Support — Not a Substitute for Clinical Judgment
Individual patient factors may require deviation from these recommendations.
Known Limitations
- SIADH is a diagnosis of exclusion
- Must rule out hypothyroidism and adrenal insufficiency first
- Vaptans have specific risks and restrictions
- Does not address pediatric SIADH
Applicable Regions
USEU
EU: ESE guidelines, tolvaptan more commonly used
US: FDA restrictions on tolvaptan duration in liver disease
Version 1Next review: 2027-01-01
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Related Resources
Frequently Asked Questions
What is the SIADH Diagnosis and Management?
The SIADH Diagnosis and Management is a management clinical algorithm for Endocrinology. It provides a structured decision tree to guide clinical decision-making, based on ESE/ESICM/ERA-EDTA Clinical Practice Guideline on Hyponatraemia + SIADH Expert Consensus.
What guideline is the SIADH Diagnosis and Management based on?
This algorithm is based on ESE/ESICM/ERA-EDTA Clinical Practice Guideline on Hyponatraemia + SIADH Expert Consensus (DOI: 10.1530/EJE-13-1020).
What are the limitations of the SIADH Diagnosis and Management?
Known limitations include: SIADH is a diagnosis of exclusion; Must rule out hypothyroidism and adrenal insufficiency first; Vaptans have specific risks and restrictions; Does not address pediatric SIADH. Individual patient factors may require deviation from these recommendations.
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