Bone Markers, Boney Metabolism

Bone is a living, growing tissue that turns over at a rate of about 10% a year. It is made up largely of collagen and calcium phosphate. Collagen is a protein that gives the bone its tensile strength and framework. Calcium phosphate is a mineralized complex that hardens the framework. This combination of collagen and calcium makes bone strong and yet flexible enough to bear weight and to withstand stress. More than 99% of the body's calcium is contained in the bones and teeth. The remaining 1% is found in the blood.

Throughout your lifetime, old bone is constantly being removed. It is replaced by new bone. During early childhood and in the teenage years, new bone is added faster than old bone is removed. As a result, bones become larger, heavier, and denser. Bone formation happens faster than bone resorption until you reach your maximum bone density and strength (peak bone mass). This happens at around age 24. After age 24, bone resorption slowly begins to happen faster than bone formation. Bone loss is most rapid in women in the first few years after menopause. But it continues into the postmenopausal years.

DISEASES THAT AFFECT THE BONE

  • Osteoporosis. Osteoporosis, or porous bone, is a disease characterized by low bone mass and structural deterioration of bone tissue. This means you may be more likely to get fractures of the hip, spine, and wrist. Osteoporosis develops when bone resorption occurs too rapidly and bone formation fails to keep up. It is more likely to develop if your bones do not achieve their optimal mass during your bone-building years. Men as well as women suffer from osteoporosis. This is a disease that can be prevented and treated.

  • Paget's disease. Paget's disease is a chronic disorder. It typically results in enlarged and deformed bones. In this disease, the breakdown and formation of bone tissue is excessive. So, bone can weaken, resulting in bone pain, arthritis, deformities, and fractures. This disease may be caused by a "slow virus" infection that is in your body for many years before symptoms appear. It may also be inherited. The disease has been known to appear in more than one family member. Paget's disease is rarely diagnosed in people under 40 years of age. Men and women are affected equally.

  • Bone metastasis. Cancer cells that leave the (primary) tumor and enter the bloodstream can take up residence in nearly every tissue of the body. Bones are one of the most common sites for these circulating cells to settle and start growing again. Metastases can occur in bones that are near or far from the primary tumor site. Metastatic bone disease is not the same as primary bone cancer. Primary bone cancer refers to a cancer that starts in bone. Bone metastasis and primary bone cancer differ in their risk factors, treatments, and outlook. Primary bone cancer is much less common than bone metastasis. Bone metastasis is one of the most frequent causes of pain in patients with cancer.

  • About half of all people who have cancer (except those with skin cancer) develop bone metastasis at some point in the course of their disease. Breast, prostate, kidney, lung, pancreas, colorectal, stomach, thyroid, and ovarian cancers account for most metastases to bones. The spine is the area most often affected by bone metastasis. It is followed by the pelvis, hip, upper leg bones (femurs), and the skull.

TESTS USED TO DETECT BONE PROBLEMS

  • Usually, bone problems are detected by measuring bone mass (density) using special types of X-rays. Bone problems can also be detected by ultrasound scans. These use high-frequency sound waves.

  • Bone markers are signs of the bone turnover process. They are sometimes used as an aid to bone density testing when doctors are evaluating whether or not you have a bone disease. The process involves measuring markers of bone resorption, such as the telopeptides, and markers of bone formation, such as bone-specific alkaline phosphatase (ALP). Bone resorption markers can be measured in blood or urine. Bone formation markers are measured in blood.

  • Most often, bone markers are used to monitor therapy for bone disease and to help your doctor determine if your body is responding to treatment. Bone markers can enable your caregiver to tell if you are responding to bone-strengthening therapy in a much shorter time period than the X-ray types of bone density testing. This way, your therapy can be altered if you are not responding properly to it.

  • There is also some evidence that bone markers can help doctors to predict which breast and prostate cancer patients are at high risk for bone metastases. Bone markers may also be able to predict a patient's response to therapy for a bone-loss condition.

  • In some cases, bone markers are ordered with other bone mineral density tests to diagnose a bone disease. Usually, however, bone markers are ordered periodically to monitor patients who already have a diagnosed bone condition and who are undergoing therapy to see how well they are responding to treatment.

Ranges for normal findings may vary among different laboratories and hospitals. You should always check with your doctor after having lab work or other tests done to discuss the meaning of your test results and whether your values are considered within normal limits.

MEANING OF TEST

Your caregiver will go over the test results with you and discuss the importance and meaning of your results, as well as treatment options and the need for additional tests if necessary.

OBTAINING THE TEST RESULTS

It is your responsibility to obtain your test results. Ask the lab or department performing the test when and how you will get your results.