A healthy 15-year-old boy undergoes routine screening. Serum alkaline phosphatase is 320 U/L (upper limit of adult range 130 U/L). Calcium, phosphate, liver enzymes, and GGT are all normal. The most appropriate explanation for this finding is:
- A Subclinical cholestasis with enzyme induction of the hepatic isoenzyme
- B Early vitamin D deficiency causing secondary hyperparathyroidism
- C Increased osteoblastic activity during the pubertal growth spurt ✓
- D Renal phosphate leak leading to compensatory bone resorption
Correct answer: C. Increased osteoblastic activity during the pubertal growth spurt
Explanation
Alkaline phosphatase is produced by osteoblasts during active bone formation, so levels are physiologically high throughout childhood and peak during the adolescent growth spurt, sometimes reaching two to three times the adult upper limit. Normal calcium, phosphate, and liver enzymes exclude rickets and cholestasis. C key discriminating point is the normal GGT: an isolated ALP rise with normal GGT points to the bone rather than the hepatobiliary source.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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