Hyponatremia is associated with confusion when serum sodium falls below which threshold?

• A. >140
• B. <120
• C. 125-130
• D. 130-135

Answer: (B)

Hyponatremia affects the brain because a lower extracellular sodium concentration creates a hypoosmolar state, causing water to move into brain cells and leading to cerebral edema. The symptoms of hyponatremia progress with severity. Mild hyponatremia (roughly 130–134 mEq/L) may cause nonspecific symptoms like nausea, malaise, or headache. Moderate hyponatremia (around 125–130) can produce confusion, dizziness, and irritability as the brain starts to lose its ability to function smoothly. Severe hyponatremia, especially when serum sodium drops below about 120 mEq/L, is when more pronounced CNS manifestations such as marked confusion, disorientation, seizures, and even coma occur due to more significant brain swelling and impaired neuronal function. Therefore, confusion is most closely associated with serum sodium falling below 120 mEq/L, which is why that threshold is the best answer. The other ranges represent milder hyponatremia where confusion is less likely to be the presenting feature.