What serum sodium level defines hypernatremia?

• A. 140 mEq/L
• B. 145 mEq/L
• C. 150 mEq/L
• D. 155 mEq/L

Answer: (B)

Hypernatremia means the serum sodium concentration is higher than what the body normally maintains. The defining feature is that the value exceeds the upper end of the normal range, reflecting a free-water deficit or an excess of sodium intake. When sodium is high, water shifts out of cells, including brain cells, leading to cellular dehydration and symptoms that range from thirst and restlessness to confusion or seizures in severe cases. The goal in management is to raise water gently to restore balance without causing rapid shifts that could harm the brain.

In the given options, hypernatremia is indicated by the value that lies beyond the normal upper limit for serum sodium. Values within the normal range do not define hypernatremia, while clearly elevated values indicate hypernatremia, with higher levels generally signaling greater risk.