What your sodium level means
Sodium is the most abundant electrolyte in your blood, and one of the most tightly regulated — a mineral that governs the body's water balance and helps nerves and muscles work. It sits on most metabolic panels, and it's a number people often misread. Here's what it measures, the typical range, what specific values mean, and when a high or low sodium is worth a closer look.
Quick reference: for the typical range at a glance, see sodium in our blood test results library, or see normal ranges for every marker.
This is general educational information, not medical advice. An abnormal sodium — especially a markedly high or low value, or one changing quickly — needs interpretation by a clinician alongside your other results and history.
What sodium measures
Sodium is an electrolyte — a charged mineral that sits mostly in the fluid outside your cells, where it's the main determinant of how much water the body holds. The blood test measures the concentration of sodium in that fluid, and the body defends this concentration within a remarkably narrow band by adjusting water, not salt: when sodium concentration rises, you feel thirsty and the kidneys hold onto water; when it falls, the kidneys let water go.
That's the single most important thing to understand about the sodium result: it's a water-balance marker, not a salt-intake marker. A low sodium usually means too much water relative to sodium, and a high sodium usually means too little water — neither is a readout of how much salt you ate. Eating more or less salt mostly changes your fluid volume and blood pressure, not the sodium concentration on your panel.
Like the other electrolytes, sodium is read in context — alongside your hydration, your kidney function, your medications, and the rest of the metabolic panel.
Typical range
A common adult reference range is:
- ~135–145 mmol/L
Values within this narrow band are considered normal, and the range is broadly the same for men and women (mmol/L and mEq/L are equivalent here). Reference ranges differ slightly between laboratories, so read your result against the range printed on your own report.
What specific sodium numbers mean
People often arrive with one figure in mind — a sodium of 133, or 145, or 148. The bands below are a rough guide to how far outside the range a value sits, not diagnostic thresholds. What the number means depends on your hydration, your medications, your kidney function, and — importantly — how fast it changed.
| Sodium (mmol/L) | How it's usually read |
|---|---|
| Below 130 | Low (hyponatremia) — worth a clinician's review, especially if it fell quickly or comes with symptoms |
| 130–135 | Mildly low — a value like 133 is a mild hyponatremia; common, often a fluid-balance issue |
| 135–145 | Within the typical range; a value like 145 sits at the top of normal |
| 145–148 | Borderline / mildly high (hypernatremia) — usually a water deficit; check hydration |
| Above 148 | Markedly high — reflects a clearer water deficit and warrants prompt review |
The key caveat with sodium is that how fast it changed matters as much as the number. A sodium of 130 that has been stable for months is read very differently from a 130 that dropped in a couple of days, because it's the rate of change that most affects the brain. So a mild, stable low in someone who feels well is often simply monitored, while a rapidly shifting value — high or low — gets attention regardless of how far it is from the range.
What a low sodium means (hyponatremia)
A low sodium means the sodium in your blood is more diluted than usual — a story about water, most of the time. It's the most common electrolyte abnormality. The usual contributors:
- Too much water relative to sodium — from overhydration, or from the body holding onto water (as in the condition called SIADH).
- Medications — some diuretics and certain antidepressants are common culprits.
- Heart, liver or kidney disease — conditions that disturb fluid balance.
Because a marked or fast-falling sodium affects the brain, it's read alongside your symptoms (headache, nausea, confusion), your medications and your fluid status rather than on its own.
What a high sodium means (hypernatremia)
A high sodium almost always means a water deficit — the body has lost more water than sodium, concentrating what remains. The usual driver is dehydration, particularly in people who can't easily drink to their thirst. It's much less often about eating too much salt. A high sodium is read alongside your hydration, urine output and kidney markers, and marked values warrant prompt attention.
The salt myth
It's worth stating plainly, because it trips up so many people: your blood sodium level does not tell you how much salt you eat. The body guards the sodium concentration so tightly — by moving water in and out — that dietary salt mostly changes your fluid volume and blood pressure instead. That's why a high sodium points to a water problem (usually dehydration), not to your diet, and why cutting salt isn't the fix for a high reading. The number on your panel is a hydration gauge first and foremost.
Sodium and potassium together
Sodium and potassium are the two headline electrolytes, reported side by side on a metabolic panel because both track the body's fluid and mineral balance and both lean on the kidneys. They answer different questions: sodium is mostly about water balance, while potassium is about cellular and cardiac stability. Reading them together — with the kidney markers — gives a fuller picture than either alone. See what your potassium level means for the companion marker, and what your creatinine and eGFR results mean for the kidney context both electrolytes depend on.
Why the trend and context matter
A single sodium is a snapshot, and with sodium the trend is especially telling, because the rate of change matters as much as the value. A sodium slowly drifting down alongside a new medication tells a different story from a stable low that's been there for years. See how to read your blood test results for the broader approach, and albumin, ALP and the metabolic panel for how the wider panel fits together.
When to talk to a doctor
A mild, stable sodium just outside the range, with no symptoms, is common and often simply monitored. It's worth prompt medical attention when the sodium is markedly high or low, when it has changed quickly, when it comes with symptoms like headache, nausea, confusion, weakness or seizures, or when you take medications known to affect it. In those cases sodium should be read in the context of your hydration, kidney function, medications, symptoms and history — not on its own.
For the typical range and a plain-English summary, see sodium in our blood test results library. For how the whole panel fits together, see how to read your blood test results and browse the rest of the Quanome blog.
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Frequently asked questions
What is a normal sodium level?
A typical adult range is roughly 135–145 mmol/L (mEq/L). Values within this narrow band are considered normal. Sodium is read alongside your hydration, kidney function and the rest of the metabolic panel rather than on its own. Always check your result against the reference range printed on your own report.
Is a sodium level of 145 high?
A sodium of 145 mmol/L sits right at the top of the normal range, so it's best described as borderline rather than clearly high. Anything above 145 is called hypernatremia and usually reflects a water deficit — most often mild dehydration rather than eating too much salt. A single 145 in someone who feels well and isn't dehydrated is commonly unremarkable, and it's read alongside your hydration on the day and your kidney markers.
What does a sodium of 133 mean?
A sodium of 133 mmol/L sits just below the usual bottom of the range (about 135), so it's a mild hyponatremia — a mildly low value. Mild lows are common and often reflect fluid balance rather than a serious problem: drinking a lot of water, certain medications, or conditions affecting the heart, liver or kidneys can all nudge sodium down. It's read in the context of your symptoms, medications and hydration, and a mild, stable 133 in someone who feels well is often just monitored.
What does low sodium (hyponatremia) mean?
Low sodium means the sodium in your blood is more diluted than usual — which is usually a story about too much water relative to sodium, not too little salt. Common causes include overhydration, certain medications (including some diuretics and antidepressants), and heart, liver or kidney disease. It's the most common electrolyte abnormality, and marked or rapidly falling lows are taken seriously because they affect the brain.
What does high sodium (hypernatremia) mean?
High sodium almost always means a water deficit — the body has lost more water than sodium, concentrating what's left. Dehydration is the usual driver, especially in people who can't easily drink to thirst. It's much less often caused by eating too much salt. A high sodium is read alongside your hydration, urine output and kidney function, and marked values warrant prompt attention.
Does my sodium level show how much salt I eat?
No — this is a common misconception. Your blood sodium level is mainly a measure of water balance, not salt intake. The body defends the sodium concentration tightly by adjusting how much water it holds onto, so eating more or less salt shifts your fluid balance and blood pressure far more than it shifts the sodium number on your panel. A high or low sodium points to a water-balance issue, not to your seasoning habits.
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