With the increased use of bone density measurements, osteoporosis can now be diagnosed and treated more easily. This has led to intense interest in the scientific community in biochemical markers of bone metabolism. Bone is constantly being recycled, resorbed, and remodeled. Osteoclasts carry out bone resorption, and osteoblasts carry out bone formation. Osteoporosis is a common disease of postmenopausal women and is associated with increased bone resorption and reduced bone formation. The result is the formation of thin, weak bones prone to fractures. Osteoporosis is now increasingly recognized in older men. Early diagnosis allows for therapeutic intervention and prevention of bone fractures.
Bone density measurement is a valuable tool in determining osteoporosis, but it cannot detect small changes in bone metabolism. Although bone density measurements can be used to monitor the effectiveness of treatment, it may take years to detect measurable changes in bone density. However, biochemical Bone Turnover Markers (BTMs) can identify any changes within a few months of applying a successful treatment. In addition, the cost of measuring BTMs is generally lower than the corresponding cost of measuring bone density.
Because levels of biochemical Bone Turnover Markers vary depending on the time of day and bone tumors, their measurements are not used as routine tests to detect osteoporosis. Their uses are beneficial in evaluating treatment efficacy by comparing the corresponding values before treatment commences. BTM levels are reduced by the use of anti-absorption drugs (e.g., estrogen, bisphosphonates, calcitonin, and raloxifene). Biochemical Indicators of Bone Metabolism have been shown to accurately predict bone density and treatment efficacy while helping document patients' compliance with treatment.
N-Telopeptides and C-Telopeptides (NTx and CTx) are protein fragments of type 1 collagen, making up almost 90% of the organic portion of bone. These proteins' C- and N-terminals are crosslinked to provide the bone strength needed. When bone is absorbed, CTx and NTx are released into the bloodstream and excreted in the urine. These serum fragments' levels correlate very well with their corresponding urine measurements when creatinine clearance is co-evaluated. The measurement of these fragments can be used to assess treatment response (within 3 to 6 months) and are good indicators of bone resorption.
Like NTx, the amino-terminal propeptide of Procollagen 1 (P1NP) is directly proportional to the new collagen osteoblasts produce. Its concentration increases in patients with various bone diseases characterized by increased osteoblast activity. Measurement of P1NP is the most effective indicator of new bone formation and is particularly useful in monitoring bone formation and anti-absorptive therapies.
Osteocalcin, or Bone G1α Protein (BGP), is a non-collagenous bone protein synthesized by osteoblasts. It enters the bloodstream during bone resorption and formation and is a good marker of bone metabolism. Serum levels of osteocalcin are correlated with bone destruction and formation (bone turnover). Elevated levels are associated with increased bone loss. Osteocalcin is a vitamin K-dependent protein. Reduced vitamin K intake is associated with reduced levels of osteocalcin. This may explain the pathophysiology of vitamin K-dependent osteoporosis.
Deoxypyridinoline (DPD, D-Pyrilinks) is formed during the maturation of type 1 collagen during the formation of new bone. During bone resorption, these molecules are released into the circulation and then excreted in the urine without further metabolism.
Bone Fraction of Alkaline Phosphatase or Ostase (BSAP) is an alkaline phosphatase isoenzyme found in the osteoblast cell membrane. It is an indicator of osteoblast metabolic status and bone formation.
These biochemical Bone Turnover Markers cannot estimate the risk of bone fracture like bone density can. However, they are essential in evaluating the effectiveness of osteoporosis treatment.
Biochemical Bone Turnover Markers can also be used to monitor the activity and treatment of Paget's disease of bone, hyperparathyroidism, and bone metastases. Biochemical Bone Turnover Markers are usually elevated in children due to increased bone resorption associated with the growth and remodeling of the ends of long bones. Their levels peak at approximately 14 years of age and then gradually decline to adult values. Because estrogen is a potent inhibitor of osteoclastic activity (bone resorption), bone density loss begins soon after the onset of menopause. Therefore, levels of biochemical markers increase after menopause.
What Do Pathological Rates Mean?
- Increase: Osteoporosis, Paget's bone disease, advanced bone tumors (primary or metastatic), acromegaly, hyperparathyroidism, hyperthyroidism.
- Decrease: Hypothyroidism, cortisone therapy, effective osteoporosis treatment
Important Note
Laboratory test results are the most critical parameter for diagnosing and monitoring all pathological conditions. Between 70 to 80% of diagnostic decisions are based on laboratory tests. Correctly interpreting laboratory results allows a doctor to distinguish "healthy" from "diseased."
Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be analyzed based on each case and family history, clinical findings, and the results of other laboratory tests and information. Your physician should explain the importance of your test results.
At Diagnostiki Athinon, we answer any questions you may have about the test you perform in our laboratory and contact your doctor to ensure you receive the best possible medical care.
