Osteocalcin test: what the result means

Osteocalcin is a small protein produced by osteoblasts — the cells responsible for forming new bone tissue. Most of the osteocalcin stays in the bone matrix, but a small part enters the blood, so the amount in blood reflects how actively the process of bone formation is happening. Osteocalcin belongs to the group of bone turnover markers — alongside it, bone alkaline phosphatase (a bone formation marker) and beta-CrossLaps (a bone breakdown marker) are often tested as well. These indicators are used to assess how quickly bone is renewed, and not bone density — a separate test, a bone density scan (DXA), is used for that. The amount of osteocalcin depends on age, sex, hormonal status (especially the sex hormones) and on vitamin D and calcium metabolism, so the result is always assessed together with the clinical picture and other tests, and not on its own.

• To assess the rate of bone turnover alongside other bone markers (bone alkaline phosphatase, beta-CrossLaps)
• To follow, over the longer term, the effect of treatment that acts on bone turnover (together with the follow-up tests chosen by the doctor)
• As an additional test in the context of osteoporosis or other bone turnover disorders, when the activity of bone formation needs to be assessed
• In research and in specialist endocrinology diagnostics

• Blood is usually taken in the morning, fasting, because the amount of osteocalcin in blood varies through the day
• It is worth telling your doctor about the supplements you take (especially vitamin D and calcium) and about recent bone fractures or operations, because these can affect the result

A raised result: what it can mean

Osteocalcin is produced by osteoblasts — the same cells that also produce another bone formation marker, bone alkaline phosphatase (BALP). Because of this, a raised osteocalcin can be caused by the same processes that also raise BALP: the healing of a bone fracture, Paget's disease, osteoblastic bone tumours, osteomalacia or hyperparathyroidism. Osteocalcin is cleared mainly by the kidneys, so impaired kidney function also raises its level in the blood.

• Healing of a bone fracture
• Paget's disease (a disorder of bone turnover)
• Osteoblastic bone tumours
• Osteomalacia (softening of the bones)
• Hyperparathyroidism
• Impaired kidney function (osteocalcin is cleared mainly by the kidneys)

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

• Bone alkaline phosphatase (BALP) and beta-CrossLaps tests, to get an overall picture of bone turnover
• Calcium, phosphorus, vitamin D and parathyroid hormone (PTH) tests
• Bone imaging tests, if Paget's disease or a tumour is suspected

The source cited for this section describes the causes of a raised total alkaline phosphatase (ALP); only the bone-related ones are kept here. Osteocalcin is produced by the same osteoblast cells, so these processes raise both markers. The effect of kidney function is based on the review “Laboratory aspects and clinical utility of bone turnover markers” (PubMed Central, PMC6053812).

A lowered osteocalcin indicates slowed osteoblast activity — much as a lowered bone alkaline phosphatase (BALP) does. Possible causes are hypothyroidism, a deficiency of protein or zinc, and inadequate nutrition. In people taking glucocorticoids (steroid medicines), osteocalcin falls in a dose-dependent way, and during effective osteoporosis treatment with medicines that reduce bone resorption, bone formation markers, including osteocalcin, also decrease.

• Hypothyroidism (reduced thyroid function)
• Protein deficiency or inadequate nutrition
• Zinc deficiency
• Taking glucocorticoids (steroid medicines)
• Osteoporosis treatment with medicines that reduce bone resorption

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

• A bone alkaline phosphatase (BALP) test, to clarify whether the decrease is related to overall osteoblast activity
• A thyroid function (TSH) test
• An assessment of nutrition

The source cited for this section describes the causes of a lowered total alkaline phosphatase (ALP) and does not single out bone alkaline phosphatase (BALP). Osteocalcin is produced by the same osteoblast cells, so these processes lower both markers. The effect of glucocorticoids is based on the Endotext chapter “An Overview of Glucocorticoid-Induced Osteoporosis” (NCBI Bookshelf, NBK278968), and the effect of treatment that reduces bone resorption on a systematic review of bone turnover markers in monitoring osteoporosis treatment (NCBI Bookshelf, NBK261650).

Related bone tests

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