Bone turnover markers: defining a therapeutic target

[Extract] Bone turnover markers (BTM) in widespread clinical use include urine NTX, plasma βCTX and plasma total procollagen type 1 amino terminal propeptide (P1NP). An important application of BTMs is in monitoring anti-osteoporosis therapy, and specifically, in indicating whether current therapy is likely to achieve optimal reduction of fracture risk. Of the 3 BTMs mentioned above, only urine NTX (as NTX/creatinine ratio) has an evidence-based threshold indicating optimum fracture risk reductio. However measurement of βCTX and P1NP is preferred owing to their smaller biological variation and greater response to treatment. We recently published provisional therapeutic thresholds for plasma βCTX assays that were equivalent to the urine NTX/creatinine ratio indicative of maximal fracture risk reduction for patients treated with risedronate