C-Telopeptide (CTx) as a Marker of Bone Resorption
C-telopeptide (CTx) is a biochemical marker of bone resorption that reflects the breakdown of type I collagen during osteoclastic bone destruction. 1
What CTx Measures
CTx is released when type I collagen in bone degrades during the bone resorption process, serving as a direct indicator of osteoclastic activity. 2, 3
The marker reflects whole-body bone metabolism and ongoing rates of osteolysis or bone breakdown throughout the skeleton. 2
CTx can be measured in both serum (s-CTx) and urine (u-CTx), with both forms correlating well with bone resorption activity. 4, 5
Clinical Contexts Where CTx is Elevated
Postmenopausal women show 86% higher CTx levels compared to premenopausal women, reflecting the accelerated bone loss associated with estrogen deficiency. 4
Patients with metastatic bone disease and elevated bone resorption markers have an increased risk for skeletal-related events (SREs) and poor outcomes. 1
Multiple myeloma patients with lytic bone lesions demonstrate elevated CTx levels, reflecting changes in bone metabolism associated with tumor growth. 1
Osteoporotic patients with vertebral and hip fractures show moderately to greatly increased CTx concentrations compared to healthy postmenopausal women. 5
Erosive osteoarthritis of the hands shows much higher CTx values than nonerosive osteoarthritis, indicating early bone involvement. 6
Periodontal disease demonstrates elevated CTx levels that correlate with radiographic bone loss and microbial pathogens. 7
Clinical Utility and Limitations
Despite associations between CTx and skeletal complications, current guidelines do NOT recommend using CTx to guide or monitor bone-modifying therapy in routine clinical care outside of research protocols. 1, 8
CTx has significant biological variability (15-40%) and is affected by time of day, fasting status, menstrual cycle, seasonal changes, and renal or liver function. 2, 8
Postmenopausal women with CTx greater than mean + 2 SD of premenopausal values have an 8-fold more rapid bone loss rate and 1.8-fold increased fracture risk. 4
No randomized controlled trials using skeletal-related events as primary endpoints have demonstrated clinical utility of CTx for monitoring treatment response, despite several studies showing decreases in CTx after bisphosphonate administration. 1
Interpretation Pattern
Elevated CTx indicates increased bone resorption and active bone loss, particularly when combined with low bone formation markers (P1NP), representing an uncoupled high-turnover osteoporotic state requiring immediate anti-resorptive therapy. 9
Low CTx (below reference range) suggests suppressed bone resorption, often seen with bisphosphonate or denosumab therapy. 2
CTx provides complementary information to bone mineral density (BMD) testing but cannot replace structural assessments or provide site-specific skeletal information. 1, 9