Hydroxyproline (4-hydroxyproline) is a non-proteinogenic amino acid formed by the post-translational hydroxylation of proline. Hydroxyproline is a major component of collagen, where it serves to stabilize the helical structure. Because hydroxyproline is largely restricted to collagen, the measurement of hydroxylproline levels can be used as an indicator of collagen content. Conditions that increase collagen turnover can elevate serum and urine hydroxyproline levels. Urine and serum hydroxyproline levels can be used as a marker for bone resorption.
