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Electrolytes
Sodium (Na)
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Sodium is the principal extracellular cation and determinant of plasma osmolality. Serum sodium reflects water balance rather than total body sodium.
Reference interval
| Conventional (mEq/L) | SI (mmol/L) | |
|---|---|---|
| Adults | 135–145 mEq/L | 135–145 mmol/L |
Specimen: Serum or plasma · Conventional × 1 = SI
Causes of high values
Hypernatraemia: water loss exceeding intake (inadequate intake, fever, diarrhoea, osmotic diuresis, diabetes insipidus) and, less often, sodium excess.
Causes of low values
Hyponatraemia: SIADH, diuretics (especially thiazides), heart failure, cirrhosis, nephrotic syndrome, adrenal insufficiency, hypothyroidism, vomiting or diarrhoea with hypotonic replacement, and hyperglycaemia (translocational).
Pre-analytical and method notes
Interpret with osmolality, volume status and urine studies. Hyperglycaemia lowers measured sodium (see corrected sodium); severe hyperlipidaemia or hyperproteinaemia gives pseudohyponatraemia with indirect ion-selective electrodes. Reference limits vary slightly by laboratory; correction speed in severe disorders follows local guidelines.
Related calculators
References
- Rifai N, Horvath AR, Wittwer CT. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Elsevier, 6th edition (2018) — Tier 3 (textbook)
- Loscalzo J, et al.. Harrison's Principles of Internal Medicine. McGraw-Hill, 21st edition (2022) — Tier 3 (textbook)
- Brenner and Rector's The Kidney. Elsevier, 11th edition (2019) — Tier 3 (textbook)
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