INTER AND INTRAINDIVIDUAL VARIATIONS IN URINARY-EXCRETION OF PYRIDINIUM CROSS-LINKS OF COLLAGEN IN HEALTHY-YOUNG ADULTS

Objectives: To investigate the inter-and intra-individual variation in the excretion of pyridinium crosslinks of collagen in first morning v oid urine samples in healthy young adults. Design: An observational st udy in which urinary pyridinium crosslinks of collagen were measured i n fasting first void urine samples over five consecutive days. Setting : The study was conducted in the Department of Nutrition, University C ollege, Cork, Ireland. Subjects: A total of 17 healthy young adults (1 1 females and 6 males) aged 22-26 y were recruited from University Col lege, Cork. The subjects were without any history of bone or articular disease, and with no intake of medicine that could affect bone or car tilage metabolism Results: There were large intra-individual variation s in the excretion of both pyridinoline (Pyr) and deoxypyridinoline (D pyr) in first morning void urine samples and the ratios of intra-to in ter-individual variation were high. In comparison, inter-individual va riation in excretion of crosslinks was relatively low. No significant day-to-day variation was observed either in Pyr or Dpyr excretion when either five, four or three consecutive days or four or three non-cons ecutive days of urine sampling were used. However, there were signific ant differences between any two consecutive or non-consecutive days in both Pyr and Dpyr excretion. Conclusions: The relatively large day-to -day variation in urinary excretion of the pyridinium crosslinks empha sises the need to use multiple samples to characterise the crosslink e xcretion of an individual. The present study demonstrates that urine s ampling for these crosslinks necessitates at least a 3 d collection to ensure that day-to-day effects are not a significant source of variat ion included in the data analysis.