On May 10, 2010, in Minerals, Tests, by Andrea

Osteocalcin is one of those strange labs that we recommend that no one seems to know what it is — including, I think, some of the docs that may or may not actually order it.

Because it is one of the more obscure labs, many docs will not actually run it for you, but let’s go over it to explain what it is, why it’s important, and why it’s gaining ground in the lab-work field.

Remember that ranges are just that — ranges.  Nothing is set in stone, and each lab sets their own range.  Your mileage may vary.

This is a fasting test.

Osteocalcin is a protein found in bone and dentin and is secreted by osteoblasts and is thought to be an important part in the bone mineralization and calcium ion exchange process.

As a lab value, it’s used as a biochemical marker for the bone formation process.  Those with higher serum osteocalcin levels correlate with increases in bone mineral density (BMD), and has been used as a biomarker for effectiveness of bone formation treatment medications.

Range is dependent on age and sex:

Adult males: 3-13 ng/mL
Adult premenopausal female: 0.4 – 8.2 ng/mL
Adult postmenopausal female: 1.5-11 – ng/mL
Children 2-17: 2.8-41 ng/mL
Neonates: 20-40 ng/mL

It should be noted that adult males will have varying readings as much as 5-10 ng/mL over a 24-hour period.  The highest value is at night and the lowest is in the afternoon.

From Bakerman’s ABC’s of Interpretive Laboratory Data, Fourth Edition:

Biochemical markers of bone turnover are potentially useful for diagnosis and monitoring efficacy of therapy in various conditions:

  • Bone Metastases
  • Paget’s Disease
  • Anticonvulsant Therapy
  • Rheumatoid Arthritis
  • Osteoporosis

Other factors that can increase bone loss include estrogen deficiency, hyperthyroidism, hyperparathyroidism, myeloma, recent fracture, or immobilization.  Chronic glucocorticoid therapy depresses bone turnover; biomarkers may not reflect true bone loss.  Young women with menstrual due to athletics or eating disorders may have high bone turnover and elevated markers of bone resorption.  Urinary markers are difficult to interpret in renal failure.

During normal bone formation, osteoblasts produce bone matrix components including type I collagen, osteocalcin, sialoproteins, proteoglycans, and alkaline phosphatase.  Type I collagen fibers accumulate and pyrdinolinium cross0links are formed.  FInally, the collagen substructure is mineralized.  Components of bone formation or resorption are released into the circulation during bone remodeling, and may be detected in blood and urine.  Markers of bone formation and resorption are given here:

  • Bone Formation (Serum)
    • Bone Specific Alkaline Phosphatase
    • Osteocalcin
  • Bone Resorption (Urine)
    • Hydroxyproline
    • Collagen Cross Links
      • Pyridinolines/Deoxypyridinolines
      • N- and C- Telopeptides

Osteocalcin (Serum): Osteocalcin is synthesized primarily by osteoblasts.  This noncollagenous protein, specific for bone and dentin, is incorporated into the extracellular matrix of bone.  This test is a marker of bone turnover when formation and resorption are coupled, and is a marker of bone formation when these processes are uncoupled.

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