by Dr. Joseph Debé
There has been a breakthrough in the prevention of osteoporosis. It is a newly available laboratory test that measures compounds in the urine, which correlate with the rate or magnitude of bone loss. Before describing the application of this test, I would like to give some general information on osteoporosis.
Bone is a living dynamic tissue. It consists of mineralized connective tissue and two general types of cells: osteoblasts, which build bone, and osteoclasts, which break down bone. Throughout life, there is a constant remodeling of bone by the action of the osteoblasts and osteoclasts. During the first two or three decades of life, the rate of osteoblast activity exceeds that of osteoclast with a resultant increase in bone density. Around the age of 30 or so, most people begin to lose bone as the osteoclasts begin to break down more bone than their counterparts produce. When the density of the bone falls below a certain threshold it is termed osteoporosis. In this state, the bones have thinned to the point that they are very susceptible to fracture. A third of American women beyond 60 years of age have spinal compression fracture. The spinal bones are particularly prone to osteoporosis. Additionally, in excess of 300,000 hip fractures secondary to osteoporosis occur annually in the United States. Hip fractures in the elderly are often a death sentence as they lead to complications from immobility, such as pneumonia.
Many abnormal physiologic states and disease processes can contribute to osteoporosis. Genetics, diet, lifestyle, and medication all influence bone health. Most cases of osteoporosis occur in women and are associated with menopause. However, a woman's rate of bone loss increases greatly between ages 40 to 44, well before menopause. In fact, a woman can lose a significant amount of bone before reaching menopause. And although bone loss can be slowed and even reversed in some cases, it is much easier to prevent, rather than treat osteoporosis.
There are testing procedures available, which can measure the density of the bones. If a low value is obtained, that indicates an immediate increased risk of fracture. The limitation of this test is apparent when a normal bone density is measured. This test gives a static "snapshot" evaluation of bone density but does not supply any information as to future risk of osteoporosis. It is possible to have both normal bone density and a rapid rate of bone loss at the same time. The bone density test will not pick up a problem until a significant amount of bone has been lost.
Analysis of urine for end products of bone breakdown can now supply this missing information. Pyridinium (Pyd) and deoxypyridinium (D-Pyd) are compounds that are found in the connective tissue of bone. As bone is resorbed, these com- pounds are eliminated in the urine. High levels of Pyd and D-Pyd in the urine have been found to very accurately indicate an accelerated rate of bone loss. Now when bone density test results are normal, Pyd and D-Pyd can be measured to assess future risk to osteoporosis.
As previously stated, it is more prudent to prevent, rather than treat, osteoporosis. A great application for this test is for the woman who is just beginning to lose bone (roughly age 30). If results are within normal range, the test can be repeated every year or so. If concentration of Pyd and D-Pyd are excessive, then various treatments can be instituted to reduce bone loss. And within just a couple of weeks of making a dietary or lifestyle change, the test can be repeated to monitor the effectiveness of treatment. It will show changes in bone loss that quickly! This preventive approach can greatly reduce the risk of osteoporosis.
This test also offers important information for the postmenopausal female with normal bone density. For several years after menopause, virtually all women have accelerated bone loss. In one out of three women, this rapid loss may continue for 15-20 years and put her at increased risk for osteoporosis. If urinary concentration of Pyd and D-Pyd remain elevated in spite of comprehensive conservative intervention, a woman may more comfortably make the decision to begin hormone replacement therapy.
Urine analysis for Pyd and D-Pyd is a simple procedure. It is also accurate, non-invasive, inexpensive, and usually insurance reimbursable.