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Sodium Blood Test: What Your Results Mean

Sodium is the primary electrolyte in the fluid outside your cells (extracellular fluid). It regulates fluid balance, blood pressure, and nerve and muscle function. Your kidneys tightly control sodium levels by adjusting how much is excreted in urine. Sodium imbalances — whether too high or too low — can have serious effects on the brain, heart, and muscles.

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Normal Range

136 – 145 mmol/L

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Unit

mmol/L

What Your Results Mean

Normal

A normal sodium level indicates that your body's fluid balance is well regulated. The kidneys and hormonal systems (particularly ADH and aldosterone) are working effectively to maintain the right concentration of sodium in your blood.

High

High sodium (hypernatraemia) usually reflects dehydration — not enough water relative to sodium — or excessive sodium intake. It can cause intense thirst, confusion, muscle twitching, and in severe cases, seizures or coma. It may also result from conditions that impair the kidneys' ability to retain water, such as diabetes insipidus.

Low

Low sodium (hyponatraemia) is the most common electrolyte imbalance in clinical practice. Causes include overhydration, syndrome of inappropriate ADH secretion (SIADH), heart failure, liver cirrhosis, kidney disease, and certain medications such as diuretics or SSRIs. Symptoms range from nausea and headache to confusion and seizures.

Frequently Asked Questions

What causes low sodium? expand_more
Common causes include drinking too much water (overhydration), SIADH, heart failure, liver disease, kidney disease, and diuretic or SSRI medications. Hyponatraemia is the most frequent electrolyte disorder seen in hospitalised patients.
What causes high sodium? expand_more
Hypernatraemia is usually caused by dehydration (insufficient fluid intake or excessive fluid loss through sweating, diarrhoea, or vomiting), diabetes insipidus, or — less commonly — excessive salt intake.
What is the normal sodium level? expand_more
Normal blood sodium is 136 to 145 mmol/L. Values outside this range — particularly below 130 mmol/L or above 150 mmol/L — require prompt medical evaluation.
Can I raise or lower my sodium through diet? expand_more
Diet affects sodium to some extent, but the kidneys finely regulate blood sodium levels regardless of intake. Sodium imbalances in the blood are almost always caused by water balance disorders rather than salt intake alone — treatment targets the underlying mechanism.
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