Beta-CrossLaps (CTX) test: what the result means (β-CTX)

Bone is constantly renewed — old parts of bone tissue are broken down (resorption) and new bone forms in their place. Beta-CrossLaps (β-CTX, C-terminal telopeptide of type I collagen) is a fragment released when bone collagen is broken down, and it enters the bloodstream — so the amount in blood reflects how actively the process of bone breakdown is happening at that time. It is one of the so-called bone turnover markers, alongside which P1NP (a bone formation marker) and osteocalcin are often mentioned. Unlike a bone density (DXA) scan, which shows the current bone density, β-CTX shows the process — whether bone is being lost faster than it is being rebuilt at that moment. The level varies through the day (highest in the morning) and depends on eating, so the conditions of the test (the time, fasting) matter when comparing results over time. Because of this variation, β-CTX is most often used not for a one-off diagnosis but to follow change — for example, whether osteoporosis treatment is working.

• To follow whether osteoporosis treatment (for example with bisphosphonates) is reducing bone resorption — a repeat test after a few months of treatment
• Together with a bone density (DXA) scan, when additional information about the rate of bone turnover is needed
• When increased bone turnover from an endocrine cause is suspected (for example a thyroid or parathyroid disorder)
• To assess fracture risk together with other indicators and a DXA scan, at a specialist's decision
• To monitor patients previously diagnosed with osteopenia or osteoporosis

A raised Beta-CrossLaps level indicates increased bone resorption (breakdown). During treatment for osteoporosis, a CTX that stays raised or is rising may mean that the antiresorptive treatment is not working or is not being taken as prescribed; bone turnover can also be driven by hormonal disorders, for example hyperprolactinaemia, or by the naturally lower amount of oestrogen after menopause.

• Poor adherence to antiresorptive treatment (for example bisphosphonates) or an insufficient response to it — CTX stays raised or rises instead of falling
• Hyperprolactinaemia (a raised prolactin level), which may stimulate osteoclast activity through a shift in the RANKL/osteoprotegerin balance
• Naturally higher bone turnover in women after menopause, because of the reduced amount of oestrogen

What to discuss with a doctor when the result is raised:

• Discussing with the doctor whether the prescribed osteoporosis treatment is working and whether its schedule is being followed
• A repeat CTX test after a few months of treatment, compared with the baseline value
• Prolactin, calcium and vitamin D tests, if a hormonal cause is suspected
• A bone density (DXA) scan, to assess the overall picture

A lowered Beta-CrossLaps level most often indicates suppressed bone resorption — this is the expected result when osteoporosis is treated with antiresorptive medicines (bisphosphonates). A significant fall in CTX within 3–6 months of treatment is considered a sign of a response to treatment.

• Effective antiresorptive treatment (for example with bisphosphonates), which lowers bone turnover markers, CTX among them, within 3–6 months — this is the expected sign of a response to treatment
• Long-term, marked suppression of bone turnover during bisphosphonate use — a very low CTX is associated with a higher risk of bisphosphonate-related osteonecrosis of the jaw

What to discuss with a doctor when the result is low:

• Discussing with the doctor whether the fall in CTX matches the expected response to treatment
• Before a planned invasive dental procedure (for example a tooth extraction), telling the doctor about long-term bisphosphonate use
• A bone density (DXA) scan, to assess the overall effectiveness of treatment

Related bone tests

Beta-CrossLaps is one of the bone turnover markers. Related indicators covered on this site: calcium, vitamin D, parathyroid hormone, osteocalcin, bone alkaline phosphatase and TRAP. Which of them is relevant in a particular case is decided by the doctor.