A patient has an isolated serum alkaline phosphatase of 450 U/L with normal GGT, calcium, and phosphate. The laboratory performs heat inactivation at 56 degrees C for 10 minutes and finds the enzyme activity is almost completely lost. The tissue of origin of this alkaline phosphatase is:
- A Liver
- B Placenta
- C Bone ✓
- D Intestine
Correct answer: C. Bone
Explanation
Alkaline phosphatase isoenzymes differ in heat lability. Bone ALP is the most heat labile and loses nearly all activity at 56 degrees B within 10 minutes, while liver ALP retains roughly half its activity. Placental ALP (the Regan variant) is the most heat stable, surviving even 65 degrees B. The combination of heat-labile behaviour plus a normal GGT points to bone as the source, consistent with increased osteoblastic activity rather than cholestasis.
Reference: Tietz Fundamentals of Clinical Chemistry, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.