What is the reference range commonly cited for alkaline phosphatase activity in U/L?

• A. 20-60 U/L
• B. 30-90 U/L
• C. 50-120 U/L
• D. 70-150 U/L

Answer: (B)

Alkaline phosphatase reference ranges come from what’s observed in healthy individuals and they vary with age, physiology, and the testing method. For adults, a widely cited benchmark is about 30 to 90 U/L. This range reflects typical nonpregnant adult values and matches what many clinical laboratories report as the standard reference interval.

Keep in mind that ALP has multiple sources (bone, liver, intestine, placenta), so levels can rise with bone growth in children or during pregnancy due to placental isoenzymes, and different assays can yield slightly different cutoffs. That’s why labs always provide their own reference interval.