E2b.4. Laboratory Assays: Bone formation markers (osteocalcin, procollagen type-I N-terminal propeptide [P1NP]) and bone resorption markers (β C-terminal telopeptide of type 1 collagen [β-CTX]) correlate strongly with rates of bone formation and resorption respectively and provide powerful data as they reflect the average bone turnover globally across all bone surfaces in the body. The disadvantage of these markers is that they reflect the final state at the time of sampling and not conditions at any other time point in the experiment.