Bone Metabolism Assays

PTH²

• Enhances calcium absorption in the intestines by stimulating the renal synthesis of 1,25(OH)2vitamin D
• Increases the amount of calcium in the blood through the release of PTH and the removal of calcium from the bone
• Decreases the amount of calcium by releasing less PTH

Vitamin D²

• Helps to form and maintain strong and healthy bones by increasing the amount of dietary calcium absorbed by the intestines
• Stops the parathyroid gland from secreting parathyroid hormone, which would increase levels of calcium in the blood
• Protects against osteoporosis, cancer, and hypertension

Osteocalcin³

• Protein that binds to calcium; it is manufactured by the osteoblasts in bone and dentin
• A highly specific marker of late stage osteoblastic activity
• Higher serum-osteocalcin levels are relatively well correlated with increases in bone mineral density

Pyrilinks-D⁴

• Excreted in urine and is a specific marker of bone resorption and osteoclastic activity.
• Used along with other bone markers to diagnose bone diseases such as osteoporosis, bone metastatis, and Paget's disease
• Useful in monitoring treatments that contain bone-active agents such as estrogens and bisphosphonates.

Calcium and phosphorous are the most abundant minerals found in the body, and the majority of both minerals are found in the skeletal system. Calcium regulation is required for many basic body functions, such as cell function, bone structure, blood clotting, and neural transmission. Insufficient calcium or loss of calcium is called hypocalcemia, whereas too much calcium in the blood, often a result of malignancy or primary hyperthyroidism, is called hypercalcemia. The body regulates calcium through the parathyroid hormone (PTH) and vitamin D, and, to a lesser extent, calcitonin.

Osteoporosis (“porous bone”) is a bone disease that increases the risk for fracture. It is caused by the loss of bone density from losing too much, not making enough, or a combination of both. Bone metabolism is the constant process of the body removing old bone (“bone turnover”) and replacing it (“bone resorption”). These processes take place in the osteoblasts, which form new bone, and osteoclasts, which break down old bone. As long as these processes are in balance, bone mass remains on a constant level. 

At mid-life, individuals begin to lose bone quicker than they are able to replace it due to calcium metabolism, calcium and vitamin D deficiency, and hormonal factors, such as changes of estrogen level. Measuring proteins produced by the osteoblasts and osteoclasts provides a real-time evaluation of bone turnover, especially in the management of post-menopausal osteoporosis. Bone resorption markers can monitor progress of therapeutic interventions within a few weeks or months, whereas bone formation markers can take 6 to 12 months. This is still an improvement over bone mineral density (BMD), which can take as long as one to two years to determine the effectiveness of treatment.