# Sodium: The salt that tracks your water balance

> Blood sodium mostly reflects your water balance, not the salt you eat. Check your result, see what low and high levels mean, and what to do next.

- Also called Serum sodium and Na
- Often on a standard checkup
- Fast for 12 hours
- Web page: https://picardo.health/guides/biomarkers/sodium

## The short answer

Sodium is the main salt in your blood. Its level mostly reflects how much water your body holds, not how much salt you eat.[1][6] Guidelines count anything under 135 mmol/L as low.[1][2]

- **A good result:** 135 to 144 mmol/L.[1][3]
- **If yours is low:** Mildly low sodium is common, often from a water pill or an antidepressant, and worth finding the cause.[1] Under 125 needs medical advice the same day.
- **Should you test?** It’s part of the standard metabolic panel. It matters most if you take a water pill, an antidepressant or a seizure medicine, especially as you get older.[1][5]

## What is a normal sodium level?

Labcorp’s range is 134 to 144 mmol/L.[3] Guidelines count anything under 135 as low, and grade it by how far it has fallen:[1][2]

| Result (mmol/L) | What it means |
| --- | --- |
| Under 125 | Very low: get medical advice today |
| 125 to 129 | Low: see a clinician soon |
| 130 to 134 | Mildly low: find the cause |
| 135 to 144 | Normal |
| 145 or more | High: usually too little water |

### Very low: get medical advice today

**Range:** Under 125 mmol/L.

Below 125, low sodium is called profound. Symptoms such as nausea, headache, confusion and, at worst, seizures become more likely.[1]

**How worried to be:** Get medical advice today. If you have a headache with nausea, or you’re vomiting, confused or very drowsy, or have had a seizure, go to an emergency department now. These can be signs of swelling in the brain.[1]

**What to do next:**

1. Don’t try to fix it yourself with salt or by drinking less. Raising sodium too fast can damage the brain, so it’s done gradually, with medical supervision.[1][2]
2. Bring a list of every medicine you take.

### Low: see a clinician soon

**Range:** 125 to 129 mmol/L.

This is moderately low.[1] Even without obvious symptoms, levels like this are linked to unsteadiness, falls and trouble concentrating.[1]

**How worried to be:** See a clinician in the next few days. If you have a headache with nausea, or you’re vomiting, confused or very drowsy, go to an emergency department now.[1]

**What to do next:**

1. Review your medicines with a clinician. Water pills, antidepressants and some seizure medicines are common causes.[1]
2. Ask whether to limit how much you drink. It depends on the cause.[1]

[Test a repeat metabolic panel, $4.00](https://app.picardo.health/labs/order?tests=322000&ref=guide-sodium)

### Mildly low: find the cause

**Range:** 130 to 134 mmol/L.

Guidelines count anything under 135 as low, though Labcorp only flags results under 134.[1][3] Even mildly low sodium has been linked to unsteadiness, falls and fractures, though it isn’t clear that sodium itself is the cause.[1]

**How worried to be:** Not urgent. Worth looking into over the next few weeks.

**What to do next:**

1. Ask a clinician to review your medicines, especially water pills and antidepressants.[1][5]
2. Recheck in a few weeks to see whether it’s stable.
3. The point is to find the cause. Guidelines don’t advise treating a mildly low number on its own.[1]

[Test a repeat metabolic panel, $4.00](https://app.picardo.health/labs/order?tests=322000&ref=guide-sodium)

### Normal

**Range:** 135 to 144 mmol/L.

Your sodium, and your body’s water balance, are normal.[1]

**How worried to be:** Nothing to worry about.

**What to do next:**

1. Nothing to do.
2. If you’re older and start a water pill, ask about a sodium check in the first few weeks.[5]

### High: usually too little water

**Range:** 145 mmol/L or higher.

High sodium usually means your body is short of water, from not drinking enough or losing fluid, rather than from eating too much salt.[3][6] Less often, a hormone problem that affects water balance is the cause.[3]

**How worried to be:** If it’s just above the range and you’ve been unwell, sweating a lot or not drinking much, drink water and recheck within a few days. If it’s well above, see a clinician today, and if you’re confused or very drowsy, go to an emergency department now.

**What to do next:**

1. Recheck within a few days.
2. If you’re thirsty all the time and pass a lot of urine, ask a clinician to look for a hormone cause.[3]

[Test a repeat metabolic panel, $4.00](https://app.picardo.health/labs/order?tests=322000&ref=guide-sodium)

## What is sodium?

> Think of blood sodium like the saltiness of soup. Add water and it tastes weaker; boil water off and it tastes stronger. That’s why the test mostly tells you about your water balance, not your salt intake.

Sodium is the main salt in your blood and the fluid around your cells. Your kidneys and hormones hold its level in a tight range, whatever you eat.[6] They do it mostly by adjusting how much water you keep, using a hormone called vasopressin.[1]

So low sodium usually means too much water for the sodium you have, not too little salt.[1]

## What causes low sodium?

- Water pills (thiazide diuretics), such as hydrochlorothiazide and chlorthalidone[1][5]
- Antidepressants, especially SSRIs, and some seizure medicines, such as carbamazepine and oxcarbazepine[1]
- Drinking far more than you need, including during long endurance events[1]
- Heart, liver or kidney failure[1]
- Your body holding on to too much water (SIADH), which can follow lung disease, some cancers, pain, nausea or surgery[1]
- Eating very little while drinking a lot, as with a diet of mostly tea and toast, or beer[1]
- MDMA (ecstasy) and desmopressin, a hormone medicine[1]
- Baxdrostat, a blood pressure medicine approved in 2026. In its trials, sodium fell below 130 in 3.7% of people on the usual dose, against 0.9% on a placebo.[4]

Water pills are the best-known cause, and the risk rises with age. In a Swedish study, about 1 in 33 women aged 80 and over who started one had sodium fall below 125 within 2 years. Under 65, the added risk was negligible.[5]

## Does salt in your diet change your blood sodium?

Barely. Your kidneys keep blood sodium steady whatever you eat, so the test can’t tell you how much salt you eat.[6]

Salt still matters for your blood pressure. US guidelines advise under 2,300 mg of sodium a day, and ideally under 1,500.[7] They also say potassium-based salt substitutes can help, unless you have kidney disease or take medicines that raise potassium.[7] In a trial of 20,995 older adults in rural China with high blood pressure or a past stroke, swapping salt for a substitute that was 25% potassium cut strokes by 14% and deaths by 12%.[8]

## How to raise low sodium

- **Changing the medicine behind it:** Water pills, antidepressants and some seizure medicines are common causes, and a clinician may switch or stop one.[1] How much it helps: a lot. How sure we are: fairly sure.
- **Drinking less, if a clinician advises it:** The usual first step when your body is holding on to too much water. It doesn’t suit every cause.[1] How much it helps: some. How sure we are: early evidence.
- **Treating the condition behind it:** Heart, liver and kidney failure can all lower sodium, and so can low cortisol from the adrenal glands.[1] How much it helps: some. How sure we are: fairly sure.

Raising sodium too fast can cause lasting brain damage, so very low levels are corrected gradually, with medical supervision.[1][2] And fixing the number isn’t the goal in itself. In a 2026 trial of 2,173 hospital patients, actively correcting low sodium brought more of them back to normal, but didn’t reduce deaths or readmissions over the next 30 days.[9]

## Who should get a sodium test?

Most people get it with routine bloodwork, as part of the metabolic panel. It’s most worth checking if:

- You take a water pill, especially if you’re older.[5]
- You’ve started an SSRI antidepressant, or a seizure medicine such as carbamazepine.[1]
- You have heart, liver or kidney disease.[1]
- You’ve become unsteady, confused or had a fall, especially when older.[1]

## How to get a sodium test, and what it costs

It comes from the comprehensive metabolic panel, which costs $4.00 through Picardo.

- [Comprehensive metabolic panel, $4.00](https://app.picardo.health/labs/order?tests=322000&ref=guide-sodium). The test this number comes from. Labcorp 322000, fast for 12 hours.

Every order comes with:

- Results in 2 to 3 days, in the app
- Physician follow-up if you want one
- Free Labcorp draw, or $75 at home
- No other fees. HSA and FSA eligible.

It’s also part of the [Base Core Annual – Men](https://picardo.health/labs/panels/base-core-men), [Base Core Annual – Women](https://picardo.health/labs/panels/base-core-women), [Heart Health](https://picardo.health/labs/panels/heart-health), [Brain Health Screening](https://picardo.health/labs/panels/brain-health), [Pregnancy](https://picardo.health/labs/panels/pregnancy), [Postpartum](https://picardo.health/labs/panels/postpartum), [Fertility](https://picardo.health/labs/panels/fertility), [Thyroid & Autoimmunity](https://picardo.health/labs/panels/thyroid-autoimmunity) and [Celiac / GI](https://picardo.health/labs/panels/celiac-gi) panels, if you’d rather test more at once.

Already have a result? [Ask Picardo about it](https://app.picardo.health/auth).

## Questions people ask

### Can drinking too much water lower your sodium?

Yes. Drinking far more than you need, as some people do during long endurance events, can dilute your blood sodium. So can very low food intake with lots of fluid, such as a diet of mostly tea and toast or beer.[1]

### Should I eat more salt if my sodium is low?

Not on your own. Most low sodium comes from holding on to too much water, not from eating too little salt, and the right fix depends on the cause.[1]

### Can low sodium cause falls?

It may. Even mildly low sodium is linked to unsteadiness, slower attention, falls and fractures. It isn’t yet clear whether sodium is the cause or a sign of other illness.[1]

### Do I need to fast for a sodium test?

Not for sodium itself. The metabolic panel it comes on asks for a 12-hour fast because it also measures glucose.

### Are salt substitutes safe?

For most people, yes, and they can lower blood pressure.[7][8] They replace some sodium with potassium, so if you have kidney disease or take a medicine that raises potassium, check with a clinician first.[7]

## Often checked alongside

- [Potassium](https://picardo.health/guides/biomarkers/potassium.md): A salt your heart and muscles depend on
- [Creatinine](https://picardo.health/guides/biomarkers/creatinine.md): Muscle waste the kidneys filter out
- [eGFR](https://picardo.health/guides/biomarkers/egfr.md): How well your kidneys filter
- [Calcium](https://picardo.health/guides/biomarkers/calcium.md): Calcium in your blood, set by the parathyroid glands

## Test details

- **Labcorp test:** Metabolic Panel (14), Comprehensive, 322000
- **LOINC:** 2951-2
- **Sample:** Blood
- **Fasting:** Not needed for sodium itself. The metabolic panel it comes on asks for 12 hours, for its glucose result.
- **Typical lab range:** 134 to 144 mmol/L[3]
- **Units:** mmol/L, the same as mEq/L

## Sources

1. Spasovski G, Vanholder R, Allolio B, et al. Clinical practice guideline on diagnosis and treatment of hyponatraemia. Eur J Endocrinol. 2014;170(3):G1–G47. https://doi.org/10.1530/EJE-13-1020
2. Verbalis JG, Goldsmith SR, Greenberg A, et al. Diagnosis, evaluation, and treatment of hyponatremia: expert panel recommendations. Am J Med. 2013;126(10 Suppl 1):S1–S42. https://doi.org/10.1016/j.amjmed.2013.07.006
3. Labcorp. Sodium, test 001198. Labcorp test menu. Accessed October 28, 2026. https://www.labcorp.com/tests/001198/sodium
4. AstraZeneca. BAXFENDY (baxdrostat) tablets: prescribing information. Initial US approval 2026. Revised May 2026. https://www.accessdata.fda.gov/drugsatfda_docs/label/2026/219878Orig1s000lbl.pdf
5. Bergh Fahlén C, Falhammar H, Skov J, Lindh JD, Mannheimer B. Thiazides and risk of hyponatremia by age and sex. JAMA Netw Open. 2026;9(4):e264642. https://doi.org/10.1001/jamanetworkopen.2026.4642
6. National Academies of Sciences, Engineering, and Medicine. Dietary Reference Intakes for Sodium and Potassium. Washington, DC: National Academies Press; 2019. https://doi.org/10.17226/25353
7. Jones DW, Ferdinand KC, Taler SJ, et al. 2025 AHA/ACC/AANP/AAPA/ABC/ACCP/ACPM/AGS/AMA/ASPC/NMA/PCNA/SGIM guideline for the prevention, detection, evaluation and management of high blood pressure in adults: a report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines. Hypertension. 2025;82(10):e212–e316. https://doi.org/10.1161/HYP.0000000000000249
8. Neal B, Wu Y, Feng X, et al. Effect of salt substitution on cardiovascular events and death. N Engl J Med. 2021;385(12):1067–1077. https://doi.org/10.1056/NEJMoa2105675
9. Refardt J, Potasso L, Pelouto A, et al. A randomized trial of targeted hyponatremia correction in hospitalized patients. NEJM Evid. 2026;5(3):EVIDoa2500086. https://doi.org/10.1056/EVIDoa2500086

Updated 2026-10-28. This is general health information, not medical advice: talk to your clinician about your results and before changing any treatment.