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Blood sodium
Last reviewed: 04.07.2025
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Reference values (norm) for sodium concentration in blood serum are 135-145 mmol/l (meq/l).
The body of a healthy person weighing 70 kg contains 3500 mmol or 150 g of sodium. 20% of this amount is concentrated in the bones and does not directly participate in metabolism. The largest part of sodium is almost entirely in the fluid of the extracellular space.
Sodium is the main cation of extracellular fluid, where its concentration is 6-10 times higher than inside cells. The physiological significance of sodium is to maintain osmotic pressure and pH in intra- and extracellular spaces, it affects the processes of nervous activity, the state of the muscular and cardiovascular systems and the ability of tissue colloids to "swell".
Sodium is excreted by the kidneys (with urine), the gastrointestinal tract (with feces) and the skin (with sweat). Sodium excretion by the kidneys fluctuates over a wide range: 1-150 mmol/day. 1-10 mmol/day is lost with feces. The concentration of sodium in sweat is 15-70 mmol/l.
The renal mechanism of sodium regulation is the most important factor in maintaining normal plasma sodium concentrations. Many causes of hyponatremia and/or hypernatremia are related to renal dysfunction.
A significant increase or decrease in serum sodium occurs due to disproportionate losses of water and salts. These conditions may require emergency care.
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