Serum CTX: A new marker of bone resorption that shows treatment effect more often than other markers because of low coefficient of variability and large changes with bisphosphonate therapy
Hn. Rosen et al., Serum CTX: A new marker of bone resorption that shows treatment effect more often than other markers because of low coefficient of variability and large changes with bisphosphonate therapy, CALCIF TIS, 66(2), 2000, pp. 100-103
Serum CrossLaps is a new assay for measuring carboxy-terminal collagen cros
slinks (CTX) in serum. This measurement is reported to be more specific to
bone resorption than other measurements. However, the utility of this and o
ther markers in monitoring patients on antiresorptive therapy depends on ho
w often changes anticipated with therapy exceed changes attributable to ran
dom variability. In a study where subjects received either placebo or pamid
ronate, we calculated the minimum significant change (MSC), that is, the ch
ange that was sufficiently large that it was unlikely to be due to spontane
ous variability. We also examined the changes in markers of bone turnover i
n subjects treated with pamidronate (APD) (30 mg I.V. in 500 mi D5W over 4
hours) to see how often observed changes in turnover after treatment exceed
ed the MSG. The MSC for serum CTX was 30.2%, and was significantly (P < 0.0
5) lower than the MSC for urinary NTX (54.0%), and not significantly differ
ent from the MSC of urinary DPD (20.6%). Ninety percent of subjects treated
with APD had a decline in serum CTX that exceeded the MSG, compared with 7
4% for bone-specific alkaline phophatase (BSAP), 57% for urinary N-telopept
ide cross-links (NTX), and 48% for free deoxypyridinoline. Changes in serum
CTX correlated reasonably well with changes in spine BMD after 2 years (r
= 0.47), but this correlation did not quite reach statistical significance
because of the small number of subjects. In conclusion, the serum CTX assay
shows greater utility for assessing efficacy of antiresorptive treatment t
han some previously described markers.