How is corrected sodium calculated in the setting of hyperglycemia, and what is the clinical significance?

• A. Corrected Na ≈ measured Na + 1.6 mEq/L per 100 mg/dL glucose above normal; this helps assess true sodium status and guide fluid therapy.
• B. Corrected Na = measured Na − 1.6 per 100 glucose.
• C. Corrected Na is not affected by glucose.
• D. Corrected Na = measured Na + 4.

Answer: (A)

Hyperglycemia raises plasma osmolality and pulls water out of cells into the extracellular space, which dilutes serum sodium and creates a misleading hyponatremia. To estimate the true sodium level if glucose were normalized, you add a correction factor to the measured sodium. The standard approximation is about 1.6 mEq/L for every 100 mg/dL of glucose above normal. So, corrected sodium is roughly measured Na plus 1.6 times the amount glucose exceeds 100 mg/dL. This correction helps you assess the patient’s real sodium status and guides fluid therapy, ensuring you don’t misjudge the severity of hyponatremia or choose inappropriate treatment.

For example, if the measured sodium is 132 mEq/L and glucose is 300 mg/dL (200 mg/dL above normal), the correction adds about 1.6 × 2 = 3.2, giving a corrected Na around 135 mEq/L. This can change management decisions, such as the choice and rate of fluid resuscitation.

The other ideas aren’t correct because subtracting the correction would misrepresent the osmotic effect, claiming no relation to glucose ignores the dilutional mechanism, or applying a fixed 4 mEq/L addition isn’t consistent with the glucose-dependent correction used in practice.