Sodium

The normal reference range for Sodium is Sodium is tightly regulated at 135-145 mmol/L. It is really a measure of water balance rather than salt intake — an abnormal sodium usually reflects too much or too little body water relative to sodium, not how much salt you eat.. Reference ranges may vary between laboratories, so always consult your healthcare provider for interpretation.

Important for nerve and muscle function, blood pressure regulation, and fluid balance.

High sodium (hypernatraemia) almost always means a water deficit rather than too much salt — inadequate fluid intake (especially in the elderly or unwell), excessive water loss through fever, sweating or diarrhoea, or the rare condition diabetes insipidus where the kidneys cannot conserve water. It causes thirst, confusion and, when severe, drowsiness and seizures.

Low sodium (hyponatraemia) is one of the most common electrolyte problems. Causes include SIADH (inappropriate water retention, often from medications, lung or brain conditions), heart, liver or kidney failure, diuretics, drinking excessive water, an underactive thyroid, and adrenal insufficiency. Symptoms range from nausea and headache to confusion and seizures when it falls quickly or far.

Sodium is part of the routine UEC panel and is measured whenever fluid balance, kidney function or electrolytes are assessed. When abnormal, paired blood and urine osmolality and a clinical fluid-status assessment are used to find the cause. It is monitored in heart failure, on diuretics, and in acute illness.