What is the reference range for serum sodium?

• A. 135-145 mmol/L
• B. 120-130 mmol/L
• C. 150-160 mmol/L
• D. 100-110 mmol/L

Answer: (A)

Normal serum sodium helps regulate extracellular fluid volume and plasma osmolality, so it’s kept within a narrow range. The widely accepted reference range is about 135 to 145 millimoles per liter, which is why this value is the correct one. Values below this range indicate hyponatremia, while values above indicate hypernatremia. Since sodium is monovalent, millimoles per liter and milliequivalents per liter are numerically the same, making this range a standard reference for interpreting results.