Markers of bone resorption--measurement in serum, plasma or urine?Clin Lab. 2003; 49(5-6):203-7.CL
We compared an established urine marker (total deoxypyridinoline (DPD), related to creatinine (cr)) with a plasma marker (CTX) to evaluate whether the methods are equally suited to detect increased bone resorption in women after the menopause and to see whether both markers show normal bone resorption in postmenopausal women on hormone replacement therapy (HRT).
DPD in first morning void urines was measured by an automated HPLC system. CTX ("beta-CrossLaps") was measured on the automated electrochemiluminescence analyzer E170 (Roche Diagnostics, Germany). For CTX, EDTA plasma and serum samples taken from fasting patients in the morning between 08.00 and 08.30 were analyzed. 49 women were premenopausal, 43 women were postmenopausal without HRT, and 13 women were postmenopausal on HRT (mostly on oral medication) for more than six months.
RESULTS AND DISCUSSION
Inter-assay coefficients of variation (CVs) at three different concentrations were 6.0%, 6.7% and 7.2% for the assay of DPD and 2.58%, 1.83% and 1.99% for CTX, respectively. CTX was more stable in EDTA plasma than in serum. 21/43 (49%) of postmenopausal women without HRT showed increased DPD/cr ratios and 19/43 (44%) showed elevated CTX concentrations. Regarding postmenopausal women on HRT, DPD/cr ratios were elevated in 3/13 women, whereas plasma CTX showed levels within the premenopausal range in all 13 women. It is discussed that in some cases a lower muscle mass as a result of increasing age or as a result of oral HRT might increase the urinary DPD/cr ratio by lowered excretion of cr. This effect would raise the number of cases with an elevated DPD/cr ratio after the menopause out of proportion.
CTX is determined with very high precision on the E170. CTX, if measured in EDTA plasma samples from fasting patients in the morning, seems to indicate bone resorption in women on HRT correctly as normal. The DPD/cr ratio in urine of women on HRT is increased in some cases above normal, presumably by lowered excretion of cr. According to our results, plasma (or serum) markers of bone resorption seem to be preferable over cr-related urine markers.