Sodium

A serum sodium test measures the amount of sodium, your body's main electrolyte, in the liquid part of your blood. For most healthy adults, the normal range falls between 135 and 145 mEq/L.

Ranges vary between labs, so compare to the range on your own lab report.

What sodium measures

Sodium is the primary electrolyte outside your cells, and it does the heavy lifting of controlling fluid balance. It works with your kidneys and hormones to keep the right amount of water in and around your cells, and it also supports nerve signaling and muscle function. Because your body guards sodium concentration tightly, your result reflects the balance between sodium and water rather than salt alone.

What high or low levels mean

A high sodium level, called hypernatremia, usually points to a water problem rather than too much salt. Common causes include dehydration, not drinking enough fluids, excessive water loss from diarrhea or fever, or occasionally excess salt intake. Symptoms can include intense thirst, confusion, restlessness, and muscle twitching.

A low sodium level, called hyponatremia, often means you have too much water relative to sodium. It can stem from overhydration, certain medications like diuretics or antidepressants, heart or kidney problems, or hormonal issues affecting water balance. Symptoms may include headache, nausea, fatigue, confusion, and in severe cases seizures. If your result sits outside the range or you have symptoms, follow up with your clinician to find the cause.

Sodium FAQ

What does it mean if your sodium is slightly high?

A mildly high sodium level most often reflects dehydration. Drinking more water and rechecking usually helps, but persistent elevation should be evaluated by a clinician to rule out other causes.

Can drinking too much water lower sodium?

Yes. Taking in large amounts of water quickly can dilute your blood sodium and cause hyponatremia. This is more likely during endurance exercise or with certain medical and hormonal conditions.

Should you worry about a sodium level of 133?

A level of 133 mEq/L is mildly low and often not dangerous on its own. Your clinician will look at your symptoms, medications, and other labs before deciding whether any action is needed.

Read alongside your potassium, chloride, and carbon dioxide (bicarbonate) results for a fuller picture of your electrolyte and fluid balance.

Sources

• MedlinePlus Medical Encyclopedia, Sodium blood test. U.S. National Library of Medicine.

• Medscape, Serum Sodium: Reference Range, Interpretation.