What is a sodium test?
A serum sodium test measures sodium (Na+) in your blood. Sodium regulates fluid inside and outside cells, blood pressure, nerve impulses and muscle function. It is tightly controlled by your kidneys, ADH (antidiuretic hormone) and aldosterone. Sodium is routinely included in any electrolyte or metabolic panel.
Sodium normal range
| Category | Range (mEq/L) |
|---|---|
| Normal | 136 – 145 |
| Mild hyponatraemia | 130 – 135 |
| Severe hyponatraemia | < 125 (emergency) |
| Hypernatraemia | > 145 |
| Critical hypernatraemia | > 155 (emergency) |
LOW Sodium — Hyponatraemia
Hyponatraemia is the most common electrolyte disorder. The sodium is low relative to body water. Common causes: excess fluid intake, hypothyroidism, heart failure, liver cirrhosis, kidney disease, SIADH (from medications, lung infections, brain conditions), prolonged vomiting or diarrhoea with water-only replacement. Symptoms: nausea, headache (mild); confusion, seizures, coma (severe). Correction must be gradual to avoid osmotic demyelination.
HIGH Sodium — Hypernatraemia
Hypernatraemia usually means water depletion relative to sodium. Common causes: dehydration, fever, excessive sweating, diarrhoea, diabetes insipidus (kidneys cannot concentrate urine). Symptoms: intense thirst, dry mouth, lethargy, confusion, muscle weakness and — in severe cases — brain shrinkage causing intracranial bleeding.
Questions to ask your doctor
- Why is my sodium abnormal?
- Is this an emergency or can it be corrected slowly?
- Do I need IV fluids or fluid restriction?
- Is a medication causing this?