What does the Sodium, Serum test measure?

Why is Sodium, Serum measured?

Serum sodium within the CMP provides the osmolar and volume status anchor of the metabolic assessment. Hyponatraemia (<136 mEq/L) — the most common electrolyte disorder in clinical practice — indicates free water excess relative to sodium from ADH excess (SIADH), hypothyroidism, adrenal insufficiency, heart failure, cirrhosis, or psychogenic polydipsia; severity classification and rate of correction determine management urgency. Hypernatraemia (>145 mEq/L) indicates free water deficit from diabetes insipidus, inadequate water intake, or excessive insensible losses. In outpatient functional medicine CMP interpretation, mild hyponatraemia in the 130–135 mEq/L range is an important finding requiring clinical cause investigation.

Reference ranges

Standard reference

136–145 mEq/L (136–145 mmol/L) # REVIEWER FLAG: Confirm Quest Diagnostics reference range for serum sodium — ranges are tightly consistent across platforms (typically 136–145 mEq/L) but confirm Quest's specific values and critical value thresholds (<125 mEq/L and >155 mEq/L).

Functional medicine optimal

138–142 mEq/L (functional medicine narrow optimal for euvolaemic, well-hydrated osmolar balance). # REVIEWER FLAG: Not standardised as a clinical guideline target — reviewer to confirm framing.

Units

mEq/L, mmol/L

Reference ranges vary by laboratory and assay platform. Interpret in context of the issuing laboratory's stated range.