What is the normal serum sodium range?

• A. 125-135 mEq/L
• B. 135-145 mEq/L
• C. 130-140 mEq/L
• D. 145-155 mEq/L

Answer: (B)

Normal serum sodium is kept in a narrow window because it helps regulate extracellular fluid balance and nerve/muscle function. The typical reference range for serum sodium is 135 to 145 mEq/L. This range is what clinicians use across laboratories as the standard for a normal value. Values below 135 indicate hyponatremia, which can lead to neurologic symptoms and, in severe cases, seizures or cerebral edema. Values above 145 indicate hypernatremia, which can cause dehydration and confusion. Among the options, 125-135 is below normal, 130-140 is not the standard normal interval and can include low values, and 145-155 is above normal. The 135-145 mEq/L range best represents the normal reference.