Sodium
Sodium is the main salt in your blood. This test shows how well your body balances water and salt.
AI-verified against cited sources. Awaiting expert reviewAlso called Na, Na+LOINC 2951-2
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What it is
Sodium is an electrolyte, a mineral that carries a small electric charge. Most of it is in the fluid outside your cells, where it helps control how much water your body holds. It also helps your nerves and muscles work. Your blood sodium level mostly reflects water balance, not how much salt you eat: it shows how much sodium is dissolved in the water in your blood. Your kidneys and a hormone called vasopressin keep it in a narrow range.
Why it matters
Sodium helps decide how much water sits inside and outside your cells, including brain cells. When sodium falls or rises fast or by a lot, brain cells can swell or shrink, which can cause headache, confusion or seizures. Small changes are common and often cause no symptoms. Sodium is read together with potassium, chloride, bicarbonate and glucose on a standard blood chemistry panel.
If it’s low
A lower sodium level usually means there is extra water in your blood, which dilutes the sodium. It is one of the most common fluid and salt imbalances in medical care. Mild cases often cause no symptoms. When the level is lower or drops fast, it can cause headache, nausea, tiredness, confusion or seizures. Many causes are common and treatable, and your clinician can sort out which one fits.
Common causes
- Some medicines, including thiazide water pills, some antidepressants and some pain relievers
- Vomiting or diarrhea
- Heart failure, liver cirrhosis or kidney disease, which can make the body hold extra water
- Drinking very large amounts of water in a short time
- Too much of the hormone vasopressin (called SIADH), which can follow some lung or brain conditions, some cancers and some medicines
- An underactive thyroid or Addison disease (an adrenal gland condition)
- Very high blood sugar, fats or proteins, which can lower the measured sodium without a true sodium shortage
- Not eating enough (malnutrition)
What can help
- Ask your clinician whether a medicine you take could be involved
- Ask whether a repeat test, or blood and urine osmolality and urine sodium tests, would help find the cause
- Talk with your clinician before changing how much you drink, because the right approach depends on the cause
If it’s high
A higher sodium level usually means your body has less water than usual compared with sodium. The most common reason is not drinking enough or losing fluid. Thirst is the main early sign. People who can't easily ask for or get a drink, such as some older adults, are most at risk. Your clinician can put your result in context.
Common causes
- Not drinking enough fluid, especially in hot weather or when thirst is weaker, as it can be in older age
- Losing water through sweating, fever, vomiting or diarrhea
- High blood sugar that makes you pass a lot of urine
- Water pills (diuretics) and some other medicines
- Kidney disease, or diabetes insipidus (uncommon), where the body can't hold on to water
- Some hormone conditions, such as problems with the adrenal glands (less common)
What can help
- Ask your clinician whether dehydration, high blood sugar or a medicine could explain a higher result
- Ask whether a repeat test or a kidney check would help
- If you are vomiting, have diarrhea or can't keep fluids down, contact your clinician
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
For adults: 135–145 mmol/L. Source: Mayo Clinic Laboratories (catalog copy hosted by Schneck Medical Center), Labcorp. Labs treat below 120 mmol/L or above 160 mmol/L as urgent.
- 1+ (this one applies)135–145 mmol/L
Sources: Mayo Clinic Laboratories (catalog copy hosted by Schneck Medical Center), Labcorp
See Sodium by age and sex, with the U.S. survey numbers where they exist.
European hyponatraemia guideline: biochemical severity of low sodium (ESE/ESICM/ERA-EDTA, 2014)
- Profoundbelow 125 mmol/L
- Moderate125 to under 130 mmol/L
- Mild130 to under 135 mmol/L
If this applies to you
Sodium means a little more for some people. Open the one that fits you.
Age 65 or older
The American Geriatrics Society notes that some antidepressants, some seizure medicines, antipsychotics, diuretics and tramadol can lower sodium. It suggests checking sodium closely in older adults when these are started or the dose changes.
Taking lithium
Lithium can lower sodium. Losing salt and water, for example from heavy sweating, diarrhea, fever or some water pills, can push lithium levels up.
How common is your level?
NHANES describes the US civilian, non-institutionalized population, not a 'healthy' reference group. People with disease, on medication, fasting or not (except fasting-subsample markers), smokers and so on are all included. A percentile says where a value sits among Americans of that sex and age, not whether it is normal.
Use the left and right arrow keys to read each age. Shift moves five years.
Reference data derived from CDC/NCHS National Health and Nutrition Examination Survey (NHANES), cycles August 2021-August 2023. Analysis by bloodtesttracker.com; not endorsed by CDC, NCHS or HHS.
Explore Sodium by age and sex: every percentile as a table, with a download.
What can affect your result
- How much you drink and how much fluid you lose through heat, exercise or illness
- Medicines, including water pills
- High blood sugar, which pulls water into the blood and dilutes sodium
- Very high blood fats or proteins, which can make some lab methods read sodium falsely low
- Age: older adults are more prone to high sodium because thirst can be weaker
- Lab differences: reference ranges differ by about 1 mmol/L between labs
- Very high blood fats (triglycerides) or protein can make sodium read falsely low on analyzers that dilute the sample (indirect ion-selective electrode). Blood-gas analyzers that measure undiluted blood (direct electrode) are not affected this way.
- Very high blood sugar, or mannitol, pulls water into the blood and lowers the measured sodium. This is a real shift in concentration, not a lab error.
- Serum or plasma should be separated from the cells promptly (Labcorp asks for within 45 minutes, Mayo Clinic Laboratories within 2 hours). Oxalate, EDTA and citrate tubes are not suitable (Labcorp).
- Many medicines raise or lower sodium. Tell your clinician about everything you take.
Hours to days. Sodium follows water balance, which can shift within hours, and clinicians correct low levels slowly because fast changes can harm the brain.
When to talk to a clinician
Contact the clinician who ordered the test soon if your sodium is outside your lab's range, especially if you take water pills or have had vomiting or diarrhea. Many labs treat a result below 120 or above 160 mmol/L as urgent. Call 911 or your local emergency number for confusion, a severe headache, a seizure, fainting or trouble staying awake.
Questions you could ask
- How often should my sodium be rechecked, given my health conditions and medicines?
- Could dehydration, high blood sugar or one of my medicines explain a higher result?
- Should we check my kidney function or repeat the test?
- Could one of my medicines explain a lower result?
- Which other tests, such as blood or urine osmolality or urine sodium, would help find the cause?
- Should we recheck it soon, and how soon?
Questions people ask
Does my sodium level show how much salt I eat?
Not really. Your blood sodium level mostly shows your water balance. Healthy kidneys remove extra salt, so eating more or less salt rarely moves this number on its own.
Why does my report say 134–144 when another lab says 135–145?
Each lab sets its own range using its own method and patients. Labcorp lists 134–144 mmol/L and Mayo Clinic Laboratories lists 135–145 mmol/L. The gap is only 1 mmol/L. Use the range printed on your own report first.
Can high blood sugar change my sodium result?
Yes. When blood sugar is very high, water moves out of cells into the blood and dilutes the sodium, so the measured sodium reads lower. Clinicians sometimes work out a corrected sodium to account for this. It is one reason sodium is read together with glucose.
Can drinking too much water lower my sodium?
It can, but it is uncommon in healthy people because normal kidneys can remove a large amount of water. It is more likely when someone drinks very large amounts in a short time or has a condition that makes the body hold water. Talk with your clinician before changing how much you drink.
Is mEq/L the same as mmol/L for sodium?
Yes. Sodium carries a single charge, so the numbers are the same in both units. A result of 140 mmol/L is 140 mEq/L.
Show the science and sources
Units
- 1 mmol/L = 1 mmol/L
- 1 mmol/L = 1 mEq/L
Is a change real?
Sodium naturally varies about 0.5% from test to test in the same healthy person. Between two results from the same lab, a change of roughly 2% or more is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Critical appraisal and meta-analysis of biological variation estimates for kidney related analytes (Jonker N et al., EFLM WG-BV).
For clinicians and researchers
Serum sodium reflects the ratio of sodium to water, so disorders of sodium concentration are disorders of water balance and tonicity, not necessarily of total body sodium. Most chemistry analyzers use indirect ion-selective electrodes (ISE), which dilute the sample. Marked hypertriglyceridemia or hyperproteinemia (for example, paraproteins) can displace water and cause pseudohyponatremia with normal osmolality, whereas direct ISE on undiluted samples avoids that error. Translocational hyponatremia occurs when glucose, mannitol or other osmoles pull water out of cells. The conventional correction adds about 1.6 mmol/L per 100 mg/dL (5.6 mmol/L) of glucose above normal, and a 1999 study in 6 healthy volunteers (Hillier et al.) found an average of 2.4 mmol/L, with larger drops once glucose rose above 400 mg/dL. The 2014 ESE/ESICM/ERA-EDTA guideline defines hyponatremia as sodium below 135 mmol/L and grades biochemical severity by ISE as mild (130–134), moderate (125–129) and profound (below 125 mmol/L). It classifies symptoms separately, and also classifies onset as acute (under 48 hours) or chronic. Work-up uses serum and urine osmolality, urine sodium and clinical volume status. Overly rapid correction of chronic hyponatremia risks osmotic demyelination, so sodium is monitored closely during treatment. Reference intervals: Mayo Clinic Laboratories 135–145 mmol/L (age 1 year and older), Labcorp 134–144 mmol/L. ARUP and Michigan Medicine Laboratories both call results below 120 or above 160 mmol/L.
LOINC 2951-2 (primary), 77139-4, 2947-0. Specimen: serum-or-plasma.
Sources
- Sodium, Serum (test ID NAS), Mayo Clinic Laboratories (catalog copy hosted by Schneck Medical Center)
- Sodium (test 001198), Labcorp
- Critical Values List (CORP-APPEND-0104A, Rev. 46), ARUP Laboratories (2026)
- Critical Value Policy, Michigan Medicine Laboratories (MLabs) (2025)
- Clinical practice guideline on diagnosis and treatment of hyponatraemia, European Society of Endocrinology, ESICM and ERA-EDTA (European Journal of Endocrinology) (2014)
- Hyponatremia: evaluating the correction factor for hyperglycemia, American Journal of Medicine (1999)
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.