What is the normal osmolal gap range?

• A. 5-10
• B. 0-5
• C. 10-15
• D. 15-20

Answer: (A)

The osmolal gap shows how much of the serum osmolality comes from unmeasured solutes. It’s the difference between the measured osmolality and the calculated osmolality (based on sodium, glucose, and BUN). Small variability in measurement and in the calculation means a normal gap isn’t zero, and in most labs a practical normal range is about 5 to 10 mOsm/kg. Values within this range are not due to abnormal substances, while a larger gap suggests unmeasured osmoles such as alcohols or toxins. Therefore, 5–10 mOsm/kg is considered the normal range.