Bedside Snapshot
- Normal (Adult)
- 135–145 mEq/L (135–145 mmol/L)
Labs vary; use the range on your report - Critical Values
- <120 or >160 mEq/L (<120 or >160 mmol/L)
Typical; lab-specific - High Suggests
- Water loss: insensible, osmotic diuresis (glucose, mannitol)
- Diabetes insipidus (central or nephrogenic)
- Hypertonic saline or sodium bicarbonate given
- No access to water: intubated, altered mental status, infants
- Low Suggests
- Diuretics, vomiting, diarrhea, burns, third spacing
- SIADH, heart failure, cirrhosis, nephrotic syndrome
- Polydipsia, beer potomania
- Pseudohyponatremia: high lipids or protein
- Hyperglycemia: true fall; correct Na⁺ for glucose
- Act Now If
- Severe symptoms (seizure, coma, GCS 8 or less, vomiting, cardiorespiratory distress): airway, glucose, 3% saline, Na⁺ at 20 min. Na⁺ <120, no severe symptoms: treat cause, medical direction, serial Na⁺. Na⁺ >160: medical control or ED
- Watch Out For
- Overcorrection (over 10 mEq/L in 24 h, or 8 in any later 24 h) can cause osmotic demyelination days later. Check Na⁺ 20 min after each bolus, then at 1, 6 and 12 h, and hourly until stable.
Reference & Critical Ranges
Lab-specific ranges: Every lab sets its own interval, by analyzer and population. Your report's range wins. The values below are typical.
Reference ranges
| Population | Conventional | SI | Notes |
|---|---|---|---|
| Adult | 135–145 mEq/L | 135–145 mmol/L | 1 mEq/L = 1 mmol/L for sodium |
| Children | Lab pediatric interval | — | Use the lab's pediatric interval; neonates vary more |
Severity & critical values
| Level | Conventional | SI | What it means |
|---|---|---|---|
| Mild hyponatremia | 130–134 mEq/L | 130–134 mmol/L | Often asymptomatic; ESE 2014 classification by sodium |
| Moderate hyponatremia | 125–129 mEq/L | 125–129 mmol/L | Severity is set by symptoms, not the number alone (Section 3) |
| Profound hyponatremia | <125 mEq/L | <125 mmol/L | Symptoms become more common below 125 mEq/L |
| Hypernatremia | >145 mEq/L | >145 mmol/L | Thirst and mental status are the first clues |
| Critical | <120 or >160 mEq/L | <120 or >160 mmol/L | Typical lab panic values; lab-specific |
Critical values: Typical panic values are <120 or >160 mEq/L (lab-specific). A patient with severe symptoms is treated on the symptoms. The number is one input.
Conversion: Sodium is monovalent, so 1 mEq/L equals 1 mmol/L. Nothing to convert.
Calculated serum osmolality
2 × Na⁺ + glucose ÷ 18 + BUN ÷ 2.8 (mOsm/kg; glucose and BUN in mg/dL)
Calculated normal runs about 275–295 mOsm/kg. Effective osmolality (urea excluded) under 275 mOsm/kg is one SIADH criterion.
Glucose-corrected sodium (Hillier)
Na⁺ + 2.4 × (glucose − 100) ÷ 100 (glucose in mg/dL)
At glucose 100 mg/dL there is nothing to correct. When glucose runs high, use the corrected value.
Free water deficit (hypernatremia)
Total body water (L) × (Na⁺ ÷ 140 − 1)
Total body water is a fraction of body weight. Use 0.6 for non-elderly men, 0.5 for non-elderly women and elderly men, and 0.45 for elderly women.
Causes of Abnormal Results
Low (hyponatremia, Na⁺ <135 mEq/L)
| Mechanism | Common causes | Bedside clue |
|---|---|---|
| Pseudohyponatremia (isotonic) | High lipids or protein (hyperlipidemia, paraproteinemia, IVIG) | Normal measured serum osmolality; no true water excess |
| Hyperglycemic (hypertonic) | Uncontrolled diabetes, hyperglycemic crisis | High glucose; correct Na⁺ before treating |
| Hypovolemic | Diuretics (especially thiazides), vomiting, diarrhea, NG suction, burns, pancreatitis, peritonitis, adrenal insufficiency | Orthostasis, dry mucosa; urine Na⁺ ≤30 mEq/L suggests low effective arterial volume |
| Euvolemic: SIADH | Malignancy, CNS disease, pneumonia, pulmonary disease, pain, nausea, surgery; drugs such as SSRIs, antidepressants, carbamazepine, cyclophosphamide | Urine osmolality >100 mOsm/kg; urine Na⁺ >30 mEq/L with normal intake |
| Euvolemic: excess water | Primary polydipsia, beer potomania (low solute intake) | Urine osmolality ≤100 mOsm/kg (maximally dilute) |
| Euvolemic: exercise-associated | Overdrinking during prolonged endurance exercise | Weight gain during the event, nausea, confusion; acute onset. Ask about fluid intake |
| Euvolemic: other | Adrenal insufficiency (cortisol deficit); hypothyroidism is a rare cause | Check cortisol and TSH when other causes are excluded |
| Hypervolemic | Heart failure, cirrhosis with ascites, nephrotic syndrome, advanced CKD | Edema, ascites, raised JVP; urine studies are less reliable with kidney disease |
Symptomatic hyponatremia is an emergency: A fast fall can bring cerebral edema and herniation, and the risk is highest in acute hyponatremia (under 48 hours). Treat the symptoms first (Section 4).
High (hypernatremia, Na⁺ >145 mEq/L)
Hypernatremia is a water deficit relative to sodium, or a sodium gain. Most cases come from free-water loss without enough water intake. Thirst normally protects against it.
| Mechanism | Common causes | Bedside clue |
|---|---|---|
| Free-water loss | Fever, tachypnea, mechanical ventilation (insensible losses); diarrhea, vomiting, NG drainage | Dry mucosa, weight loss, low urine output |
| Osmotic diuresis | Hyperglycemia, mannitol, urea | High urine output with glucose or mannitol exposure |
| Diabetes insipidus | Central (trauma, surgery, tumor) or nephrogenic (lithium, hypercalcemia, hypokalemia) | Large volumes of dilute urine with rising Na⁺ |
| Impaired thirst or access | Intubation, altered mental status, infants, older adults | Cannot drink; often the main cause in ICU patients |
| Sodium gain | Hypertonic saline, sodium bicarbonate, salt ingestion, primary hyperaldosteronism (rare) | Recent IV sodium load or ingestion history |
Interpretation & Bedside Approach
Step-by-step approach
- Is it real? Check glucose and the lab's method. A high glucose, lipids or protein can lower a measured value (Section 8). Repeat when the result does not fit the patient.
- Is it hypotonic? Measure serum osmolality. Hypotonic (effective osmolality under 275 mOsm/kg) means true hyponatremia.
- How sick is the patient? Classify by symptoms (table below), not by the number alone.
- Volume status and urine studies: Assess volume at the bedside, then check urine osmolality and urine sodium on a spot sample taken with a serum sample (table below).
- Acute or chronic? Under 48 hours is acute. 48 hours or more is chronic. Acute cases risk brain edema. Chronic cases risk osmotic demyelination on fast correction.
- Escalate or dispose: Any severe symptom means hospital care with serial sodium checks. Without symptoms, the cause drives management, and monitoring follows.
Symptom severity classification
| Severity | Symptoms |
|---|---|
| Moderately severe | Nausea without vomiting, confusion, headache |
| Severe | Vomiting, cardiorespiratory distress, abnormal deep somnolence, seizures, coma (Glasgow Coma Scale 8 or less) |
Urine studies for hypotonic hyponatremia
| Test | Result | Suggests |
|---|---|---|
| Urine osmolality | ≤100 mOsm/kg | Excess water intake (polydipsia, beer potomania) |
| Urine osmolality | >100 mOsm/kg | ADH activity: SIADH, hypovolemia, hypothyroidism, adrenal insufficiency, heart failure |
| Urine sodium | ≤30 mEq/L | Low effective arterial volume (extrarenal loss, heart failure, cirrhosis) |
| Urine sodium | >30 mEq/L | Renal sodium loss: diuretics, SIADH, adrenal insufficiency, cerebral salt wasting |
Diuretic use and kidney disease change these results. Read them against the clinical picture, not on their own.
SIADH criteria
SIADH is a diagnosis of exclusion. Rule out the others first. Then check the ESE 2014 essential criteria. You need every one of them:
- Effective serum osmolality below 275 mOsm/kg
- Urine osmolality above 100 mOsm/kg at some level of reduced effective osmolality
- Clinical euvolemia
- Urine sodium above 30 mmol/L with normal sodium and water intake
- No adrenal, thyroid, pituitary or renal insufficiency; no recent diuretic use
Three findings back it up: serum uric acid below 0.24 mmol/L (4 mg/dL), serum urea below 3.6 mmol/L (21.6 mg/dL), and Na⁺ that fails to correct after a 0.9% saline infusion.
Predicting the change from an infusion
Adrogué–Madias estimate
Change in Na⁺ = (infusate Na⁺ + infusate K⁺ − serum Na⁺) ÷ (total body water + 1)
Use this estimate to plan, not to promise. Measure Na⁺ after each change. The formula misses ongoing urine losses.
Trend beats a single value: A slow fall that turns into a rapid rise sets up osmotic demyelination. Check the next value before you give the next bolus.
Management Priorities
Emergency: Symptomatic hyponatremia (seizure, coma, vomiting, cardiorespiratory distress)
- Monitor and protect: Protect the airway and breathing, and set seizure precautions. Check glucose and run continuous ECG. Treat where sodium can be checked closely.
- Hypertonic saline: One bolus of 3% saline, 150 mL IV over 20 min, as the table shows. Then check Na⁺ at 20 min.
- Target: Repeat the bolus until Na⁺ is up about 5 mEq/L in total.
- Persistent severe symptoms: If severe symptoms persist after that rise, continue 3% saline toward about 1 mEq/L per hour more, inside the limits below, until a stop criterion is met.
- Stop when: Whichever comes first: symptoms improve, Na⁺ has risen 10 mEq/L in total, or Na⁺ reaches 130 mEq/L.
- Limit: The ceiling is 10 mEq/L in the first 24 hours, then 8 mEq/L per 24 hours until Na⁺ hits 130 mEq/L. High-risk patients get a lower goal, set with medical direction.
Emergency: Overcorrection (rise over 10 mEq/L in the first 24 hours, or over 8 mEq/L in any later 24 hours)
- Stop: At once, stop the hypertonic saline and anything else that raises Na⁺ or lowers free water.
- Re-lower with expert direction: Options are electrolyte-free water (for example D5W), about 10 mL/kg over 1 hour, and/or desmopressin 2 mcg IV, no more often than every 8 hours. ESE 2014 gives these as options, so follow local protocol.
- Recheck: Check Na⁺ hourly until stable. That interval is a practice norm, since ESE 2014 sets none. Watch for dysarthria, dysphagia, weakness and seizures over the following days.
Medications
| Drug | Adult dose | Pediatric dose (max) | Onset / key notes |
|---|---|---|---|
| 3% sodium chloride | Severe symptoms: 150 mL IV over 20 min; repeat up to 2 more times until Na⁺ is up about 5 mEq/L. Moderately severe symptoms (nausea, confusion, headache): ESE 2014 suggests (weak recommendation, 2D) a single 150 mL infusion over 20 min, per protocol and medical direction. Alternative 2 mL/kg where body composition is atypical |
Not given on this page Pediatric dosing is weight-based and protocol-driven; ESE 2014 excludes children. Use the E3 pediatric formulary and medical direction |
High-alert Effect within minutes. Stop at symptom improvement, +10 mEq/L total, or Na⁺ 130 mEq/L |
| Tolvaptan (Samsca), oral | 15 mg once daily; increase to 30 mg after at least 24 hours, to a maximum of 60 mg daily. Hospital start only; no more than 30 days |
Not established in children |
Boxed warning: start and re-start in hospital; too-rapid correction causes osmotic demyelination. Contraindicated: hypovolemic hyponatremia, inability to sense or respond to thirst, anuria, strong CYP3A inhibitors, hypersensitivity, ADPKD outside REMS. Not for urgent Na⁺ rises needed to prevent or treat serious neurologic symptoms. Liver injury: limit to 30 days and stop for symptoms. Avoid fluid restriction in the first 24 hours. Concomitant hypertonic saline not recommended. ESE 2014 recommends against vaptans in moderate or profound hyponatremia; the label and ESE differ |
| 0.9% sodium chloride or balanced crystalloid | Hypovolemia: 0.5–1.0 mL/kg/h IV; adjust for overload. Give rapid fluid resuscitation first when unstable |
Protocol-based |
Restores volume and sodium. After volume restoration ADH falls and urine output can rise sharply, with a rapid Na⁺ rise; monitor urine output and Na⁺ closely. Avoid hypotonic fluids (D5W, 0.45% saline), which can lower Na⁺ further in hyponatremia |
| Urea (oral) | 0.25–0.50 g/kg per day in divided doses; second-line for SIADH |
Not routinely used (consult) |
Bitter taste; often mixed in a sachet by the pharmacy. Team-directed |
Doses are typical references. Follow local protocols, medical direction and institutional policy.
Hypernatremia: treatment principles
- Shock or hypovolemia first: give isotonic crystalloid for volume before correcting free water.
- Replace the free-water deficit: oral or enteral water if the patient can swallow; otherwise D5W or a hypotonic fluid by protocol. Deficit = total body water × (Na⁺ ÷ 140 − 1), as in Section 1.
- Limit the rate of fall: Lowering a high sodium too fast can cause cerebral edema or intracranial hemorrhage. Set the rate with medical direction, and document it.
- Monitor: Na⁺ every 4–6 hours during active correction, with neurologic checks.
- Severity follows symptoms: Thirst and altered mentation show up first. Lethargy, seizures and coma come after.
Definitive care & disposition
- Symptomatic patients: ICU or step-down, with serial Na⁺ and neurologic checks. For moderately severe cases, ESE 2014 suggests a Na⁺ check at 1, 6 and 12 hours.
- Asymptomatic or chronic moderate or profound (no severe symptoms): Stop the cause. Restrict free water as first-line where appropriate. Do not aim for fast correction. No more than 10 mEq/L in the first 24 hours, and no more than 8 mEq/L per 24 hours after that.
- Unresolved or unclear cause: If the cause stays unclear, reopen the diagnosis and bring in endocrinology or nephrology.
Field & Transport Considerations
Point-of-care testing
A point-of-care (POC) analyzer gets you a sodium fast. It may read differently from a lab serum value, so confirm with the lab once there is time. Let the serial trend and the symptoms guide the decision. A POC number is no reason to delay treatment for severe symptoms.
Before and during interfacility transport
Chart the last Na⁺ with its time and method, plus the time and volume of any hypertonic saline, the glucose, and the last drink or fluid history. Recheck Na⁺ on the schedule your protocol sets after each bolus. Isotonic fluid only. Avoid hypotonic IV fluids. A symptomatic patient needs hospital-level care and should not wait on a lab result.
| Setting | Consideration |
|---|---|
| EMS | Hypertonic saline only where protocol and medical direction allow; document the time and volume of each bolus |
| Transport | Keep the patient on continuous monitoring; treat seizures per protocol; avoid fast volume shifts |
| Receiving ED or ICU | Hand off the Na⁺ trend, the time of each dose and the target rise; the receiving team sets the correction plan |
Special Populations
| Population | What changes | Clinical implication |
|---|---|---|
| Neonates & infants | Ranges and fluid handling differ; the ESE 2014 guideline does not cover children | Use the lab's pediatric interval and pediatric protocol. See weight-based dosing |
| Children & adolescents | Hyponatremic seizures occur; hypertonic saline dosing is weight-based in many pediatric protocols | Follow pediatric protocol and medical direction; do not use adult fixed volumes |
| Pregnancy | Pregnancy physiologically lowers serum sodium and osmolality, so a mildly low value may be normal for gestation | Interpret mild values in context and do not treat a physiologic value. Involve obstetric care for symptomatic or profound values, including after oxytocin or with preeclampsia |
| Older adults | Less total body water (0.5 in men, 0.45 in women) | Use the lower body-water fraction in deficit estimates; higher risk of falls and confusion from chronic low sodium |
| CKD / dialysis | Impaired free-water excretion; urine studies less reliable | Interpret urine results with caution; involve nephrology early |
| Liver disease | Higher osmotic demyelination risk on fast correction | Use a lower correction goal than the general limit from the first 24 hours, set with medical direction; stop the trigger first |
| Alcohol use & malnutrition | Higher osmotic demyelination risk; low solute intake in beer potomania | Use a lower correction goal than the general limit from the first 24 hours, set with medical direction; add solute and nutrition as the plan allows |
Interfering Factors & Pitfalls
Collection & handling
| Factor | Effect | Why | Avoid / fix |
|---|---|---|---|
| Sample drawn above an IV line | False ↓ or ↑ | Infusate contaminates the sample | Draw from the other arm or stop the infusion and flush per lab practice |
Medications & supplements
| Factor | Effect | Why | Avoid / fix |
|---|---|---|---|
| Thiazides, SSRIs and antidepressants, carbamazepine, cyclophosphamide | True ↓ | Impair free-water excretion or raise ADH | Stop or switch when possible; monitor Na⁺ after starting |
| IVIG (protein load) | False ↓ (pseudohyponatremia) | Protein raises the solid phase of serum | Check serum osmolality; do not restrict free water for a fake low |
Physiologic & assay effects
| Factor | Effect | Why | Avoid / fix |
|---|---|---|---|
| Hyperglycemia | True ↓ (translocational) | Glucose draws water out of cells; the fall is real, not an assay artifact | Correct Na⁺ for glucose (Section 1) and treat the hyperglycemia |
| High lipids or protein | False ↓ (isotonic) | Solid phase displaces water; indirect ion-selective electrodes read low | Measure serum osmolality to confirm |
| Indirect ion-selective electrode | False ↓ (isotonic) | Serum is diluted before measurement; pseudohyponatremia still occurs with ISE | Do not assume ISE rules it out |
Common misinterpretations
- A normal sodium does not rule out a water problem. Volume status and osmolality still matter.
- Glucose 500 mg/dL with Na⁺ 130 mEq/L is a real translocational fall. Corrected Na⁺ is about 140 mEq/L. Do not give hypertonic saline or restrict water on the uncorrected value.
- Fluid restriction does not treat hypovolemic hyponatremia. Restore volume with isotonic fluid.
- A 10 mEq/L rise in the first 24 hours is a ceiling, not a goal. High-risk patients for osmotic demyelination need a lower target, set with medical direction (Section 4).
Physiology & Test Basics
What it measures
Serum or plasma sodium is the concentration of sodium in the blood's water. It tracks the ratio of total body sodium to total body water. It does not measure how much sodium the body holds in total. This page covers the concentration. Osmolality and urine electrolytes have their own pages.
Physiology & regulation
- Osmoregulation: Osmoreceptors release ADH (vasopressin) when effective osmolality rises. ADH pulls water back in at the kidney.
- Thirst: The thirst threshold sits higher than the ADH threshold. ADH acts first.
- Kidney: Over the long run, the kidney sets the balance by excreting sodium and water.
- RAAS: Angiotensin II and aldosterone hold on to sodium and build volume.
- Effective circulating volume: Low effective volume (heart failure, cirrhosis, hypovolemia) sets off ADH release.
How it is measured
Serum or plasma, with the tube type set by the lab. Most labs run an indirect ion-selective electrode on a diluted sample. When the sodium does not fit the patient, check the measured serum osmolality on an undiluted sample.
Why it matters
Sodium shifts the brain's water content fast. A falling sodium can cause cerebral edema and seizures. A rising sodium that climbs too fast can cause osmotic demyelination days later. In emergency and critical care, sodium is the main guide for fluid and hypertonic-saline decisions.
Clinical Pearls
Check volume and osmolality first: Hyponatremia is almost always a water problem. Volume status picks the treatment. Hypovolemia: restore volume. SIADH: restrict free water. Hypervolemia: treat heart failure or cirrhosis.
Symptoms set the treatment: Severe symptoms (seizure, coma, vomiting, cardiorespiratory distress) need hypertonic saline without delay. Moderately severe symptoms (nausea without vomiting, confusion, headache) call for stopping the cause. ESE 2014 weakly suggests (2D) a single 150 mL 3% infusion over 20 min, per protocol and medical direction. The aim is about 5 mEq/L per 24 hours, with Na⁺ checked at 1, 6 and 12 hours. Asymptomatic patients get the cause treated. Do not correct them quickly.
Osmotic demyelination is the hidden harm: Dysarthria, dysphagia, weakness and locked-in states can show up days after a rapid rise. High-risk patients include those with alcohol use, malnutrition, liver disease, thiazide or antidepressant use, low potassium, and long-standing hyponatremia.
Correct glucose first: High glucose pulls the measured sodium down. Calculate corrected Na⁺ before you decide on hypertonic saline.
Hypotonic fluids can make it worse: D5W and 0.45% saline pull sodium lower. For volume in hyponatremia, use isotonic fluid, unless the team is correcting hypernatremia.
Tolvaptan is a hospital drug: Start and restart it in hospital only. The label caps use at 30 days and advises against concomitant hypertonic saline. ESE 2014 recommends against vaptans in moderate or profound hyponatremia. The label and ESE differ, so follow local policy.
Low sodium after IVIG may be false: A protein load can pull the measured sodium down while true osmolality stays normal. Check osmolality before you restrict water.
References
- Spasovski G, et al. (2014). Clinical practice guideline on diagnosis and treatment of hyponatraemia. European Journal of Endocrinology, 170(3), G1–G47. https://doi.org/10.1530/EJE-13-1020
- Verbalis JG, et al. (2013). Diagnosis, evaluation, and treatment of hyponatremia: expert panel recommendations. The American Journal of Medicine, 126(10 Suppl 1), S1–S42. https://doi.org/10.1016/j.amjmed.2013.07.006
- Adrogué HJ, Tucker BM, Madias NE. (2022). Diagnosis and management of hyponatremia: a review. JAMA. https://doi.org/10.1001/jama.2022.11176
- Otsuka America Pharmaceutical. (2021). SAMSCA (tolvaptan) tablets, US prescribing information (boxed warning, indications, dosage). US Food and Drug Administration. https://www.accessdata.fda.gov/drugsatfda_docs/label/2021/022275s017lbl.pdf
- Adrogué HJ, Madias NE. (2000). Hypernatremia. New England Journal of Medicine, 342(20), 1493–1499. https://doi.org/10.1056/NEJM200005183422006
- Hillier TA, Abbott RD, Barrett EJ. (1999). Hyponatremia: evaluating the correction factor for hyperglycemia. The American Journal of Medicine, 106, 399–403. https://doi.org/10.1016/S0002-9343(99)00055-8
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- For Educational Purposes Only: This content is intended for educational reference and should not be used for clinical decision-making.
- Not a Substitute for Professional Judgment: Always consult your local protocols, institutional guidelines, and supervising physicians.
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