Hyponatremia: workup and management

Serum sodium under 135 mEq/L. Severity of symptoms, not the number alone, decides urgency. Confirm hypotonicity, classify by volume status and urine studies, and limit the rate of correction to avoid osmotic demyelination.

Working diagnosis Adult · US guidelines Draft · awaiting physician review

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01Orient

What's new in the evidence

Symptomatic hyponatremia: rapid intermittent bolus 3% saline (100 mL over 10 min, up to 3 times) is preferred over continuous infusion (SALSA, 2021)
Large cohorts (2023) found osmotic demyelination rare and slow correction associated with higher mortality, but current guidance keeps the correction limits
Proactive desmopressin 'clamp' did not reduce overcorrection compared with reactive use in a 2024 RCT; it remains a specialist option
Overcorrection rescue: desmopressin 2–4 mcg IV/SC every 6–8 hours with D5W 3 mL/kg as needed

Differential diagnoses

SIADH (drugs, malignancy, pulmonary or CNS disease, pain, nausea)
Hypovolemia (GI losses, diuretics, especially thiazides)
Heart failure, cirrhosis, nephrotic syndrome
Primary polydipsia, beer potomania, tea-and-toast diet
Adrenal insufficiency
Hypothyroidism (severe)
Pseudohyponatremia (lipids, paraproteins) or hyperglycemia

02Assess

Risk scores and decision tools

Serum osmolality, urine osmolality and urine sodium triad
ODS risk factors: Na ≤105, alcohol use disorder, malnutrition, hypokalemia, liver disease
Electrolyte-free water clearance to predict response to fluid restriction

Key history questions

Symptoms: headache, nausea, confusion, seizures, falls
Onset: known to be under 48 h (acute) or chronic/unknown
Drugs: thiazides, SSRIs, carbamazepine, oxcarbazepine, PPIs, MDMA
Fluid intake, alcohol, diet
Vomiting, diarrhea
Heart, liver or kidney disease

Examination findings

Volume status: orthostatics, JVP, mucous membranes, edema, ascites
Level of consciousness and focal signs
Signs of hypothyroidism or adrenal insufficiency

03Investigate

Initial investigations

Serum osmolality and glucose (corrected sodium)
Urine osmolality
Urine sodium
BMP, uric acid
TSH
Morning cortisol (or ACTH stimulation test if unclear)

Advanced investigations

Lipid panel and protein if serum osmolality normal
Chest imaging and head CT if SIADH without obvious cause
Urea or fractional uric acid excretion in difficult cases

04Treat

Immediate management

Severe symptoms (seizure, coma, vomiting with confusion): 3% saline 100 mL IV over 10 min, repeat up to 2 more times (peripheral line acceptable)
Aim for a 4–6 mEq/L rise in the first hours, which usually reverses severe symptoms
Check sodium after each bolus, then every 2–4 hours during active correction

First-line treatment

Correction limit: 8 mEq/L in 24 h for high ODS risk (alcohol use, malnutrition, hypokalemia, liver disease, Na ≤105); otherwise 10-12 mEq/L
Hypovolemic: isotonic saline; stop thiazides
SIADH: fluid restriction under about 1 L/day; treat the cause
Hypervolemic: fluid restriction, loop diuretics, treat HF or cirrhosis

Second-line treatment

SIADH: oral urea or tolvaptan if restriction fails (avoid tolvaptan in liver disease)
Over-correction: re-lower with D5W and desmopressin 2 mcg IV with nephrology input

Specialist referrals

Nephrology or endocrinology for severe or refractory cases
ICU for severe symptomatic hyponatremia needing hypertonic saline

05Disposition

Admission criteria

Moderate or severe symptoms
Sodium under 125 mEq/L in most cases
Needs IV therapy or close sodium monitoring

Safe discharge criteria

Chronic mild asymptomatic hyponatremia with clear cause
Stable sodium on repeat and outpatient labs arranged

Follow-up timing

Repeat sodium within 1 week of a medication or fluid change

Patient instructions

Follow the fluid restriction if given
Return with confusion, worsening headache or vomiting

Monitoring

Sodium every 2-4 h while correcting, then every 6-12 h
Urine output: a sudden large dilute diuresis signals risk of over-correction

Clinical pearls and pitfalls

Urine osmolality under 100 mOsm/kg suggests excess water or low solute intake
Urine sodium over 30 mEq/L on no diuretics points to SIADH or renal salt loss
Do not diagnose SIADH until hypothyroidism and adrenal insufficiency are excluded

RefGuidelines and landmark evidence

GuidelineUS Expert Panel – Diagnosis, Evaluation, and Treatment of Hyponatremia (2013)PublisherPubMed
GuidelineEuropean clinical practice guideline on hyponatraemia (2014)PublisherPubMed
TrialSALSA: bolus vs continuous hypertonic saline (Baek et al., 2021)Free full textPubMed
TrialSevere hyponatremia correction rate, mortality and osmotic demyelination (Seethapathy et al., 2023)PublisherPubMed
TrialProactive vs reactive desmopressin in severe symptomatic hyponatremia: RCT (2024)Free full textPubMed

For education only. Typical adult starting points; confirm doses against renal function, allergies, interactions and your institution's protocols. Not a substitute for clinical judgment or senior review.