Hyponatremia is defined as a serum sodium concentration below which value?

Hyponatremia is defined as a serum sodium concentration below which value?

• A. Na < 150
• B. Na > 135
• C. Na < 125
• D. Na < 135

Answer: (D)

Serum sodium is normally kept in a narrow range, about 135–145 mEq/L. Hyponatremia is defined as a serum sodium concentration below 135 mEq/L. This threshold captures any sodium value that falls outside the lower end of the normal range, with more severe hyponatremia occurring as sodium falls further below that point. The value of 150 as a cutoff would misclassify many people as hyponatremic, and a cutoff of greater than 135 would miss true hyponatremia. A value below 125 describes more severe hyponatremia, not the defining threshold.

Serum sodium is normally kept in a narrow range, about 135–145 mEq/L. Hyponatremia is defined as a serum sodium concentration below 135 mEq/L. This threshold captures any sodium value that falls outside the lower end of the normal range, with more severe hyponatremia occurring as sodium falls further below that point. The value of 150 as a cutoff would misclassify many people as hyponatremic, and a cutoff of greater than 135 would miss true hyponatremia. A value below 125 describes more severe hyponatremia, not the defining threshold.