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# Bone turnover markers and bone matrix proteins

Blood and urine markers show how fast bone is being built and broken down; they help follow treatment, not diagnose osteoporosis.

Updated Nov 12, 2026

## Key facts

- Formation markers come from osteoblasts: bone-specific alkaline phosphatase, osteocalcin and P1NP (the propeptide cut off when type I collagen is made).
- Resorption markers come from osteoclast activity: CTX and NTX (fragments of type I collagen), pyridinoline cross-links in urine and TRAP5b.
- They are used to check that treatment is working: CTX falls within months on antiresorptive drugs, and P1NP rises on anabolic treatment.
- Osteoporosis is diagnosed by bone density and fractures, not by these markers.
- CTX varies with time of day and food, so it is measured fasting in the morning.

## In detail

- Osteocalcin is a vitamin K–dependent protein (it needs γ-carboxylation) made by osteoblasts.
- Osteonectin binds collagen and hydroxyapatite and helps start mineralisation; osteopontin anchors osteoclasts to bone and also appears in kidney stones and inflammation.
- Osteoprotegerin, made by osteoblasts, is a decoy receptor that binds RANKL and stops osteoclast formation; the drug denosumab mimics this effect.
- Hydroxyproline in urine was an early resorption marker but depends on dietary gelatin.

**Also called**
CTX and P1NP, Osteocalcin, osteonectin and osteopontin

## Clinical notes

- A very high alkaline phosphatase with normal liver enzymes suggests a bone source: Paget disease, healing fractures, bone metastases, osteomalacia or normal growth in children.
- Markers stay high after a fracture for months, which must be considered when reading them.

## Test yourself

Think of the answer, then tap the question to see it.

## Which marker is used to confirm that an antiresorptive drug is working?

A fall in a resorption marker, usually serum CTX.

## Can bone turnover markers diagnose osteoporosis?

No. Diagnosis rests on bone density and fragility fractures; markers help follow treatment.

## What does osteoprotegerin do?

It binds RANKL as a decoy receptor and so blocks osteoclast formation and activity.

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## Connections

## Related conditions 3

- [Osteoporosis](https://durgical.com/en/conditions/osteoporosis/)
- [Paget disease of bone](https://durgical.com/en/conditions/paget-disease-of-bone/)
- [Primary hyperparathyroidism](https://durgical.com/en/conditions/primary-hyperparathyroidism/)

## Related 4

- [Alkaline phosphatase (ALP) as a lab test](https://durgical.com/en/biochemistry/topics/alkaline-phosphatase-as-a-lab-test/)
- [Vitamin K (phylloquinone)](https://durgical.com/en/biochemistry/molecules/vitamin-k/)
- [Vitamin D (calcitriol)](https://durgical.com/en/biochemistry/molecules/vitamin-d/)
- [Collagen synthesis](https://durgical.com/en/biochemistry/topics/collagen-synthesis/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Alkaline Phosphatase: MedlinePlus Medical Test](https://medlineplus.gov/lab-tests/alkaline-phosphatase/) (MedlinePlus, US National Library of Medicine, 2026).

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Source: https://durgical.com/en/biochemistry/topics/bone-turnover-markers-and-bone-matrix-proteins/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/topics/bone-turnover-markers-and-bone-matrix-proteins/