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Sodium
The electrolyte that governs the body's water balance and nerve and muscle function.
Other names: Serum sodium, NaSection: Blood chemistry
Updated: August 29, 2026·MedProtect editorial team Reference information — not a diagnosis or a prescription
In shortThe normal range for blood sodium is 135–145 mEq/L (135–145 mmol/L). Abnormal values usually reflect water balance rather than salt intake alone.
Reference ranges
Group
Reference range
Adults
135–145 mEq/L (135–145 mmol/L)
Normal value ranges vary slightly among laboratories, and some labs use different measurements or test different samples.
Check your value
Enter the number from your lab report — see how it compares with the typical range. Mind the units shown in the chosen row.
A rough comparison with a typical range, not a diagnosis. Reference ranges vary between laboratories — check the range on your own report and let a clinician interpret the result.
What this marker is
Sodium is an electrolyte — a mineral that carries an electric charge when dissolved in body fluids. It holds the body's water balance steady and keeps nerves and muscles working. Most blood sodium is measured as part of a basic or comprehensive metabolic panel, alongside potassium, chloride, and the other electrolytes.
A sodium result is really a statement about the ratio between salt and water in the body. Levels that are too high (hypernatremia) usually mean too little water relative to sodium; levels that are too low (hyponatremia) usually mean too much water diluting the sodium. That is why providers read sodium together with the other electrolytes and with the clinical picture rather than alone.
The test uses a blood sample from a vein. Recent injury, surgery, or serious illness, unusually large or small amounts of salt or fluid, intravenous fluids, and medicines such as diuretics or steroid hormones like hydrocortisone can all move the result — the provider needs that context.
Age, sex, and certain medical conditions can also nudge sodium up or down, so an out-of-range value does not automatically mean a condition that needs treatment. The number is the starting point for finding out why the balance shifted.
When it is high
Fluid loss and inadequate intakeExcessive sweating, diarrhea, burns, and not drinking enough water leave too little fluid for the amount of sodium. People who cannot recognize or act on thirst are at particular risk.
Diabetes insipidusIn this uncommon disorder the kidneys cannot conserve water, so sodium concentrates.
Adrenal gland problemsCushing syndrome and hyperaldosteronism push the sodium balance upward.
Too much salt or sodium bicarbonateAn unusually large salt or sodium bicarbonate intake can raise the level.
Certain medicinesCorticosteroids, laxatives, lithium, and pain relievers such as ibuprofen or naproxen can raise sodium.
When it is low
Conditions that hold extra waterHeart failure, certain kidney diseases, and cirrhosis of the liver increase total body water and dilute sodium; certain brain and lung diseases and some cancers act similarly.
SIADH and vasopressinWhen antidiuretic hormone is released in abnormal amounts (SIADH), or there is too much vasopressin, the body retains too much water.
Sodium lossVomiting and diarrhea remove sodium directly.
Certain medicinesDiuretics (water pills), morphine, and SSRI antidepressants can lower sodium.
Other causesAddison disease, an underactive thyroid, ketonuria from fat breakdown, high blood sugar, very high triglycerides, and malnutrition also appear on the list.
What can skew the result
These factors can shift the value without any disease — worth considering before a retest:
Recent injury, surgery, or serious illnessSalt and fluid intake, intravenous fluidsDiuretics and steroid medicinesAge and sex
How to prepare
No special preparation is usually needed. Tell your provider about the medicines you take — especially diuretics and steroid hormones — and about any recent illness, surgery, or intravenous fluids.
When a retest makes sense
An abnormal sodium is read together with the other electrolytes and repeated as needed; the provider may add urine sodium and osmolality tests to find out whether water gain or sodium loss is driving the change.
Who usually reviews this result
A result outside the reference range is usually reviewed by: your GP or primary care doctor; a nephrologist or endocrinologist depending on the suspected cause. Bring your lab report and any previous results to the appointment.
Names used on lab reports
Your report may use any of these names: SodiumNaSerum sodiumNa test
Units and conversion
Measured in: mEq/L
mEq/L=mmol/L
For sodium, 1 mEq/L = 1 mmol/L — the number stays the same, only the unit label changes. Results are rounded to 2 decimal places.
Several markers on your report?
See how MedProtect explains results in the app: the whole report, a check of the recognized values, and a clear breakdown.
Not usually. High blood sodium (hypernatremia) most often reflects too little water — from sweating, diarrhea, burns, or inadequate drinking — though a very high salt or sodium bicarbonate intake and several medicines can also raise it.
What is SIADH?
The syndrome of inappropriate antidiuretic hormone secretion: antidiuretic hormone is released in abnormal amounts or from an abnormal place, the body retains too much water, and blood sodium becomes diluted.
Is mEq/L the same as mmol/L for sodium?
Yes. For sodium, 1 mEq/L equals 1 mmol/L, so a result of 140 mEq/L is written 140 mmol/L on reports that use SI units.
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