Calculate the corrected sodium for a patient with measured Na 130 mEq/L and glucose 300 mg/dL.

• A. 131 mEq/L
• B. 132 mEq/L
• C. 133 mEq/L
• D. 134 mEq/L

Answer: (C)

Hyperglycemia creates a dilutional hyponatremia because high glucose in the extracellular space pulls water out of cells, increasing extracellular water and lowering the measured sodium. To estimate the true sodium, you correct for the hyperglycemia using a standard factor.

Using the common correction of 1.6 mEq/L increase in sodium for every 100 mg/dL glucose above 100 mg/dL:

• Glucose above normal = 300 − 100 = 200 mg/dL

• Correction amount = (200/100) × 1.6 = 3.2 mEq/L

• Corrected sodium = 130 + 3.2 ≈ 133 mEq/L

So the corrected sodium is about 133 mEq/L. This shows the hyponatremia on the lab value is in part due to hyperglycemia, and the true sodium is closer to the normal range.