Urinary pyridinoline and deoxypyridinoline, pyridinium crosslinks released during breakdown of mature collagen, might serve as useful markers of bone resorption. Before their role can be identified, reference values must be established. In this study, free pyridinoline (f-Pyr), free deoxypyridinoline (f-DPyr), and creatinine (Cr) were measured in first morning void urine samples from 250 girls and 265 boys between the ages of 4 and 10 years. Overall, there was a decrease in f-Pyr:Cr and f-DPyr:Cr ratios with increasing age in both sexes, but there was a wide range of values for individuals of similar ages. Further studies are required to assess whether urinary pyridinium crosslink excretion is suYciently deranged in conditions aVecting bone metabolism for the measurement of these compounds to be of clinical value. (Arch Dis Child 1999;80:370-373) Keywords: pyridinoline; deoxypyridinoline; bone resorption Certain biochemical markers of bone turnover might prove to be of clinical use in conditions and treatments that aVect bone metabolism. Markers of bone formation include osteocalcin, bone specific alkaline phosphatase, and propeptides derived from type I collagen, all of which have the disadvantage of requiring a serum sample for their measurement; whereas markers of bone resorption, including calcium, hydroxyproline, hydroxylysine glycosides, telopeptides and pyridinium collagen crosslinks, can be measured in urine. Until recently, urinary hydroxyproline was the best established marker of bone resorption. However, urinary hydroxyproline is influenced by dietary intake, is metabolised extensively in the liver, and is not specific for bone collagen.1 Pyridinoline (Pyr) and deoxypyridinoline (DPyr) are non-reducible pyridinium compounds that crosslink mature collagen chains within extracellular matrices and are released into the circulation during collagen resorption. Unlike hydroxyproline, urinary excretion of Pyr and DPyr is not influenced by dietary intake 1 and is more specific for resorption of bone collagen.
2In adults, ∼ 30-40% of pyridinium crosslinks appear free in urine, with the remainder in peptide form. The measurement of total urinary pyridinium crosslinks in adults has shown good correlation between Pyr and DPyr excretion and bone turnover as assessed by radioisotopic 4 and histomorphometric 5 techniques, but corresponding data in children are not available. The clinical usefulness of measuring pyridinium crosslinks in adult urine has been shown in a variety of bone diseases including rheumatoid arthritis, osteoarthritis, primary hyperparathyroidism, hyperthyroidism, Paget's disease, osteomalacia, osteoporosis, and metastatic bone disease. 6 If the urinary excretion of Pyr and DPyr is to be of any value in assessing bone resorption in conditions or treatments that might aVect bone turnover in children, then normal ranges for the excretion of these crosslinking amino acids must be established. However, there are few data on urinary pyridinium crosslink excretion in healthy children. Shaw e...
