Which of the following is a marker of bone formation?

• A. Serum calcium
• B. Serum alkaline phosphatase
• C. Serum creatinine
• D. Serum bilirubin

Answer: (B)

Serum alkaline phosphatase is a key marker of bone formation because it is an enzyme produced by osteoblasts, the cells responsible for forming new bone. When there is increased osteoblastic activity, such as during periods of bone growth or remodeling, the levels of alkaline phosphatase in the serum typically rise. This makes serum alkaline phosphatase a useful biomarker in evaluating various conditions related to bone metabolism, including osteoporosis and Paget's disease.

In contrast, serum calcium primarily reflects the level of calcium in the bloodstream and its balance, which is not a direct indicator of bone formation activity. Serum creatinine is a marker of kidney function and does not provide insight into bone health or formation. Serum bilirubin, often associated with liver function and the breakdown of red blood cells, does not have any relevance in assessing bone formation. Thus, serum alkaline phosphatase stands out as the most pertinent marker for evaluating bone formation.