What is one of the markers of bone resorption?

• A. Urine hydroxyproline
• B. Serum calcium
• C. Serum phosphate
• D. Serum alkaline phosphatase

Answer: (A)

Urine hydroxyproline is a significant marker of bone resorption because it is a byproduct of collagen breakdown, which occurs when bone is resorbed by osteoclasts. When bone is being remodeled, the collagen matrix is degraded, releasing hydroxyproline into circulation, and subsequently, it is excreted in urine. High levels of urine hydroxyproline can indicate increased bone resorption, making it a useful biomarker in assessing conditions that involve bone loss, such as osteoporosis.

In contrast, serum calcium and serum phosphate are more closely associated with bone metabolism but do not specifically indicate resorption. Serum alkaline phosphatase is primarily a marker of bone formation rather than resorption, as it is involved in bone mineralization processes.