Part 1: Understanding Osteoporosis

In your lifetime, you've got to get as much bone as you can and not lose it. The most important risk factor for osteoporosis is a low bone mass.

The upper limit of bone mass that you can acquire is genetically determined, according to the FDA's Office of Special Nutritionals. But even though you may be programmed for high bone mass, other factors can influence how much bone you end up with. For instance, men tend to build greater bone mass, which is partly why more women face osteoporosis. But there's another reason. With the decline of the female hormone estrogen at menopause, usually around age 50, bone breakdown markedly increases. This is because estrogen helps keep calcium in women's bones and maintains bone mass. For several years, women lose bone two to four times faster than they did before menopause. The rate usually slows down again, but some women may continue to lose bone rapidly. By age 65, some women have lost half their skeletal mass.

Because the changes at menopause increase a woman's risk, many physicians feel it's a good time to measure a woman's bone density, especially if she has other risk factors for osteoporosis. The best way to gauge a woman's risk for osteoporotic fracture is to measure her bone mass. Routine x-rays can't detect osteoporosis until it's quite advanced, but other radiological methods can.

The FDA has approved several kinds of devices that use various methods to estimate bone density. Most require far less radiation than a chest x-ray. Physicians consider a patient's medical history and risk factors in deciding who should have a bone density test. The method used is often determined by the equipment available locally. Readings are compared to a standard for the patient's age, sex and body size. Different parts of the skeleton may be measured, and low density at any site is worrisome.

Bone mineral density tests are useful for confirming a diagnosis of osteoporosis if a person has already had a suspicious fracture, or for detecting low bone density so that preventive steps can be taken. There's a profound relationship between bone mass and risk of fracture according to the Osteoporosis Research Center at Creighton University. Readings repeated at intervals of a year or more can determine the rate of bone loss and help monitor treatment effectiveness. However, estimates are not necessarily comparable between machine types because they use different measurement methods. You always want to go back to the same machine, if you can.

Another new test provides an indicator of bone breakdown. There is a simple, noninvasive biochemical test that detects in a urine sample a specific component of bone breakdown, called NTx. Clinical labs can get results in about 2 hours. The NTx test, marketed as Osteomark, can help physicians monitor treatment and identify fast losers of bone for more aggressive treatment, but the test may not be used to diagnose osteoporosis.