Osteocalcin
Overview
Osteocalcin measures a vitamin K-dependent protein secreted by osteoblasts during bone formation that binds calcium and incorporates into bone matrix, serving as a marker of bone turnover and mineralization. Carboxylated osteocalcin anchors in hydroxyapatite while undercarboxylated forms circulate and may influence insulin sensitivity and testosterone production. Elevated levels indicate high bone formation rates in growth or Paget's disease, while low levels suggest osteoporosis or vitamin K deficiency. Clinically, osteocalcin testing monitors antiresorptive therapy effectiveness and assesses bone metabolic activity.
Clinical Use Cases
- Monitoring antiresorptive therapy (bisphosphonates, denosumab) response.
- Evaluating bone turnover in osteoporosis treatment trials.
- Diagnosing Paget's disease of bone and metabolic bone disease.
- Assessing vitamin K status and bone health correlation.
Specimen Types
- Serum.
- Plasma (EDTA).
Measurement Methods
- Two-site immunoradiometric assay (IRMA).
- Enzyme immunoassay (ELISA).
- Chemiluminescent immunoassay.
Test Preparation and Influencing Factors
- Fasting morning sample preferred; diurnal variation exists.
- Vitamin K deficiency or warfarin therapy decreases carboxylated form.
- Renal impairment elevates circulating osteocalcin.
- Recent fractures or bone surgery transiently increase levels.
Synonyms
- Bone Gla protein (BGP).
- Osteocalcin (OC).
- Gamma-carboxyglutamic acid protein.