Correlations between biochemical markers of bone resorption and creatinine excretion

There were two reasons for doing this study. The first was to assess whether expressing biochemical markers of bone resorption as a ratio to creatinine excretion influences the correlations between them. The second was to assess whether biochemical markers of bone resorption are correlated with creatinine excretion, which is a biomarker of muscle mass. Three biochemical markers of bone resorption, free deoxypyridinoline (DPD), N-telopeptides (NTx) and C-telopeptides (CTx), together with creatinine (cr), were measured in 24-h urine samples of 45 healthy people (26 women and 19 men). The urinary concentrations of DPD, NTx and CTx were highly correlated with each other. These relationships were weakened, or no longer statistically significant, when the markers were expressed as a ratio to cr excretion. The 24-h excretion of each of the markers was correlated with 24-h cr excretion in men, but only 24-h DPD was correlated with 24-h cr excretion in the women. The men had significantly higher 24-h excretion rates of each of the markers than the women did. Since muscle mass is related to skeletal mass, these data suggest that in healthy people the rate of bone resorption may be a function of skeletal size as well as the rate of bone turnover. For small human studies 24-h urine sampling is recommended in preference to untimed sampling. However, for clinical purposes, or for large clinical trials, this may not be practical.