Markers of Bone Turn Over

Bone is constantly undergoing formation & resorption (remodeling) with the two processes occurring in equal amounts.

Markers with increased bone formation (osteoblastic activity)

• Serum alkaline phosphatase
• Osteocalcin

Markers of bone destruction (osteoclast activity)

• Urinary hydroxyproline & pyridinoline

(1) ALP

• 15-30% ALP = bone
• Remainder  =  Liver, gut & other minor sources
• Located in osteoblast membrane released during osteoblast tumour

Problem with measurement of ALP

• Special techniques are required to separate bone ALP from other isoenzymes like
• Electrophoresis
• ISO-electrofocusing
• (2) Osteocalcin or bone Gla protein (BGP)

Non-collaqenous protein syntheszed by osteoblasts & released into plasma during bone formation

Measured

Radio-immunoassay techniques

(3) Urinary Hydroxyproline

Amino acid is a component of collaguen     released & excreted in  urine during bone reabsorption

Released       Free HP     metabolized in liver & does not appear in urine

10% = in form of oligopeptide fragments       appear in urine & measured                            after hydrolysis

(4)       Pyridium cross-Links

Pyrdinoline & deoxypyridinoline are collagen arosslinks found in bone & cartilage

Bone reabsorption       released       urine            Measured by = HPLC &                                                                                                                  radioimmoassay