Sodium (Na) — Normal Range & Interpretation

Clinical Context

Sodium is the principal extracellular cation and the primary determinant of serum osmolality and extracellular fluid volume. It governs water distribution across cell membranes, neuronal excitability, and blood pressure regulation. Abnormal sodium levels produce neurologic symptoms ranging from confusion and lethargy to seizures and coma, making this one of the most clinically actionable electrolytes in primary care and acute settings.

Hyponatremia develops from SIADH, thiazide diuretics, heart failure, cirrhosis, adrenal insufficiency, psychogenic polydipsia, and hypotonic fluid administration. Hypernatremia reflects free water loss or inadequate intake, seen in dehydration, diabetes insipidus, osmotic diuresis, tube feeding without adequate water, and impaired thirst in older adults. NPs assess volume status alongside the sodium value, since treatment depends on whether the patient is hypovolemic, euvolemic, or hypervolemic.

High-yield for NP boards: recognize the classic presentations, especially SIADH in small cell lung cancer and post-operative patients, thiazide-induced hyponatremia in older women, and dehydration-related hypernatremia in nursing home residents. Expect questions on correction rates, since rapid correction of chronic hyponatremia causes osmotic demyelination. Candidates must link sodium abnormalities to mental status changes and identify medications, including SSRIs and carbamazepine, that precipitate hyponatremia through SIADH.

Related Labs

• Potassium (K) — mEq/L
• Chloride (Cl) — mEq/L
• CO2 (Bicarbonate) — mEq/L
• BUN — mg/dL
• Creatinine — mg/dL

Sources

• MedlinePlus