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CTX (C-Telopeptide of Type I Collagen), Serum

A blood marker of how fast old bone is being broken down. It is mostly used to follow osteoporosis treatment, not to screen healthy people.

AI-verified against cited sources. Awaiting expert reviewAlso called CTX, CTX-I, CTxLOINC 41171-0

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The usual range for CTX depends on sex. Choose female or male above to see where you stand.

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What it is

Bone is renewed all the time. Cells called osteoclasts break down old bone, and as they work they release small pieces of collagen into the blood. CTX is one of those pieces, so its level shows how quickly bone is being broken down. CTX changes a lot with the time of day and with meals, so it is usually drawn in the morning after an overnight fast.

Why it matters

CTX shows whether bone breakdown is running faster than usual, for example after menopause. Clinicians mostly use it to see whether medicines that slow bone loss are working, by comparing a result before treatment with one a few months later. It cannot diagnose osteoporosis on its own and does not replace a bone density scan.

If it’s low

A lower CTX means bone is being broken down more slowly. That is normal for healthy adults whose bone is stable, and it is the effect that bone-protecting medicines are meant to have. Because CTX falls after meals and through the afternoon, a low result can also just reflect when you ate or when the blood was drawn.

Common causes

  • Treatment with medicines that slow bone breakdown (the intended effect)
  • Eating before the blood draw, or a sample taken in the afternoon
  • Combined (estrogen-containing) birth control pills, which are linked to lower bone turnover markers
  • Normal variation in a healthy premenopausal adult, since lab ranges don't fit everyone

What can help

  • Ask your clinician whether the result matches what they expected from your treatment
  • If the sample was drawn later in the day or after eating, ask about repeating it in the morning after an overnight fast

If it’s high

A higher CTX means bone is being broken down faster than usual. That is expected after menopause and is common for several months after a broken bone. CTX does not show how much bone you have, so it is read together with a bone density scan, your fracture risk and your history.

Common causes

  • Menopause, when falling estrogen speeds up bone breakdown (CTX can roughly double)
  • A recent fracture (bone markers can stay raised for months)
  • Long periods of bed rest or being unable to move around
  • Osteoporosis or other conditions with fast bone turnover, such as Paget's disease of bone or an overactive parathyroid gland
  • Reduced kidney function, because CTX builds up when the kidneys clear it more slowly

What can help

  • Ask your clinician how to read this result alongside a bone density scan and your fracture risk
  • Stay active with weight-bearing exercise such as walking, and eat a diet with enough calcium and vitamin D
  • Keep alcohol moderate and avoid smoking, which are both linked to bone loss
  • Ask your clinician whether bone-protecting treatment is right for you

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

The usual range depends on sex and age. Choose women or men to see the one that applies.

Children and teens 10 ranges

See CTX by age and sex, with the U.S. survey numbers where they exist.

What can affect your result

  • Time of day: highest in the middle of the night and lowest in the afternoon
  • Eating: a meal can lower CTX by up to about 40%
  • Age and sex: stable through adult life, then roughly double after menopause; adult men run higher than premenopausal women
  • Recent fracture, long bed rest and pregnancy
  • Kidney function
  • Bone medicines and hormone therapy
  • The assay and sample type (serum or EDTA plasma), so compare results from the same lab
  • Eating lowers CTX by up to about 40%, so a sample taken after a meal can look falsely low.
  • CTX is highest in the middle of the night and lowest in the afternoon, so a late-day sample reads lower than a morning one.
  • High-dose biotin can interfere with some assays. Quest advises waiting at least 8 hours after usual daily biotin doses and at least 72 hours after mega-doses.
  • A recent fracture raises bone markers for months (up to about 6 months after minor fractures and up to a year after a hip fracture).
  • Reduced kidney function can raise CTX, because it is cleared by the kidneys, so the usual range may not apply.
  • Hemolyzed samples are rejected by labs such as ARUP and Quest. EDTA plasma is more stable than serum, and different assays give different results.

Morning, about 7:30 to 10 a.m., after an overnight fast. Quest asks for at least 12 hours of fasting and an 8 to 10 a.m. draw. Bone breakdown falls first when bone-protecting treatment starts, and bone building follows a few weeks later.

When to talk to a clinician

CTX alone is rarely urgent. Talk with your clinician if your result is well above your lab's range and you have had a recent fracture, new bone pain or loss of height, or if you take bone treatment and have not gone over the result.

Questions you could ask

  • Should I have a baseline CTX before starting any bone treatment?
  • Was my sample drawn under the right conditions, in the morning and fasting?
  • Could menopause, a recent fracture or my kidney function explain this result?
  • How does this fit with my bone density scan and fracture risk?
  • Is this the effect you expected from my bone treatment?
  • When should we recheck it, and should it be at the same lab, time of day and fasting state?

Questions people ask

Why do I need to fast and go in the morning for this test?

CTX swings during the day and drops after you eat. A fasting morning sample, usually before 10 a.m., keeps your results comparable over time. Eating can lower CTX by up to about two-fifths.

Does a high CTX mean I have osteoporosis?

No. CTX shows how fast bone is being broken down, not how much bone you have. It normally rises after menopause. Osteoporosis is judged mainly from a bone density scan and your fracture risk, and CTX is used to follow treatment.

Why is my lab's range different from another lab's?

Different CTX assays, and different groups of healthy people, give different numbers. The same blood can read differently on different assays. Compare results from the same lab and use the range printed on your report.

Show the science and sources

Units

  • 1 pg/mL = 1 pg/mL
  • 1 pg/mL = 1 ng/L
  • 1 pg/mL = 0.001 ng/mL
  • 1 pg/mL = 0.001 µg/L

Open the CTX unit converter

Is a change real?

CTX naturally varies about 15.1% from test to test in the same healthy person. Between two results from the same lab, a rise of 55% or more, or a fall of 36% or more, is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: The European Biological Variation Study (EuBIVAS): a summary report.

For clinicians and researchers

CTX is the beta-isomerized C-terminal telopeptide of type I collagen, released when osteoclasts degrade bone with cathepsin K. IOF and IFCC (2011) named serum CTX the reference marker of bone resorption, alongside P1NP for formation, and a 2025 ESCEO/IOF/IFCC update re-affirmed EDTA-plasma beta-CTX-I for monitoring osteoporosis treatment when kidney function is normal. CTX has the largest daily swing of the bone turnover markers: it peaks between about 01:30 and 04:30, roughly 40% to 60% above the 24-hour mean, and bottoms out between about 11:00 and 15:00. Food lowers it (reported falls range from about 18% to 40%), so collection between 7:30 and 10:00 after an overnight fast is recommended, and EDTA plasma is preferred for stability (National Bone Health Alliance, 2017). Automated Roche and IDS-iSYS assays use the same antibodies yet give different results, so reference intervals are assay-specific. In 637 healthy premenopausal women aged 30 to 39 in a four-country study on the Roche assay, the interval was 114-628 ng/L (pg/mL). Both beta-CTX-I and total P1NP may be raised by reduced kidney function (renal retention), and KDIGO 2017 suggests not routinely measuring collagen breakdown markers in CKD G3a-G5D, and the 2025 ESCEO/IOF/IFCC paper proposes bone-specific ALP and TRACP5b as reference markers in CKD-associated osteoporosis. Treatment targets for CTX are not firmly established. One suggestion is to return values to the lower half of the premenopausal reference interval, but the 2025 consensus calls for more studies, so no target range is given here. No published critical value was found.

LOINC 41171-0 (primary), 53092-3. Specimen: serum-or-plasma.

Sources

  1. C-Telopeptide, Beta-Cross-Linked, Serum (test 0070416), ARUP Laboratories
  2. Collagen Type I C-Telopeptide (CTx) (test code 17406), Quest Diagnostics
  3. Bone Turnover Markers: Basic Biology to Clinical Applications, Endocrine Reviews (2023)
  4. Update on the role of bone turnover markers in the diagnosis and management of osteoporosis: a consensus paper from ESCEO, IOF and IFCC, Osteoporosis International (2025)
  5. Use of CTX-I and PINP as bone turnover markers: National Bone Health Alliance recommendations to standardize sample handling and patient preparation to reduce pre-analytical variability, Osteoporosis International (2017)
  6. Markers of bone turnover for the prediction of fracture risk and monitoring of osteoporosis treatment: a need for international reference standards, Osteoporosis International (2011)
  7. The clinical utility of bone marker measurements in osteoporosis, Journal of Translational Medicine (2013)
  8. KDIGO 2017 Clinical Practice Guideline Update for the Diagnosis, Evaluation, Prevention, and Treatment of Chronic Kidney Disease-Mineral and Bone Disorder (CKD-MBD), Kidney International Supplements (2017)
  9. Osteoporosis, National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIH)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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