Biochemical markers of bone turnover may be used to evaluate derangements in bone formation and/or resorption. Studies conducted in CF patients have shown in general a decrease in markers of bone formation and increase in markers of bone resorption. Conway et al reported correlation between markers of bone turnover and both spinal and total body BMD; however, no studies have evaluated whether bone turnover markers correlate with pQCT parameters. Serum PICP is a peptide cleaved from the carboxy-terminal end of collagen type I and is a marker of bone formation. Deoxypyridinoline is a cross-linking amino acid that is released from the bone matrix by resorption, and thus is a marker of bone resorption.