What is osteoporosis?
How do I know if I have osteoporosis?
Why is a bone density test useful?
Can osteoporosis be diagnosed without a bone density test?
If I don’t get a mammogram, I could die from breast cancer, but I can’t die from osteoporosis, can I?
Why are some bone density tests done in the heel or wrist and some at the spine or hip?
How accurate are bone density tests in determining if I have osteoporosis?
If a bone density measurement in my heel gives a T-score value of -1.5, will this be the same for my spine?
If I start therapy, do I need any special bone density tests?
If I am already being treated for osteoporosis or taking hormone replacement therapy, why should I have a bone density test?
Do bone density tests use x-rays?
Do men get osteoporosis?
How do we interpret QCT results?
What is osteoporosis?
Osteoporosis is a disease where bones break even though you are not doing anything out of the ordinary. These so-called “fragility fractures” happen when the amount of bone is not enough to withstand the pressures from simple tasks, such as picking up a bag of groceries or a grandchild, or when you slip and fall and your wrist or hip breaks, where it would not have broken when you were younger. While spine, wrist and hip fractures receive the most attention in osteoporosis, many people believe that if you simply fall down and break any bone, then you have or are at risk for having osteoporosis.
How do I know if I have osteoporosis?
If you have had a broken bone recently from a minimal trauma, such as falling down or bending over to lift something up, you probably have osteoporosis. If you broke your ankle skydiving, you probably don’t have osteoporosis. Not everybody who is at risk of breaking their bones actually does so it usually takes at least a little fall or injury to break the bone, and some people are more careful than others. However, just because you haven’t broken a bone in the last year doesn’t mean that it couldn’t happen. Just like a person with very high cholesterol levels has a high risk of heart attack, it might not happen to all of them in the next month, or year, or 5 years, but eventually it usually does. People with osteoporosis have an increased risk of having a fracture, even if it doesn’t happen right away. One way to identify these people is to measure how much bone they have.
Why is a bone density test useful?
A bone density test measures how much bone you have. The size and density of a bone influences strongly whether or not it will break, so measuring the density of a bone can be used to estimate its risk of breaking. However, there is no need to measure the density of every bone in the body. Osteoporosis is a global disease that affects the whole skeleton, some parts more than others, but all to some extent, so that measuring any one bone helps to estimate your overall risk for fracture.
Can osteoporosis be diagnosed without a bone density test?
If you have a fracture from a simple fall, that is a good indicator that you have osteoporosis. But you don’t want to wait until you have a fracture to find out if you might be at risk. There are many factors that increase your risk of having osteoporosis—if your mother or grandmother had it, if you smoke, if you have low body weight, or if you had low estrogen levels or low dietary calcium intake earlier in life—but a measurement of low bone density is the single most predictive factor for osteoporosis.
If I don’t get a mammogram, I could die from breast cancer, but I can’t die from osteoporosis, can I?
More women in the US die from osteoporosis and its complications each year than from breast, uterine, and cervical cancer combined. It’s not the fall and broken hip that kills, it’s the pneumonia after being laid up for months, or the infection after surgery, or the disability that leads to other complications. Osteoporosis is a preventable disease, and if detected early can be treated successfully.
Why are some bone density tests done in the heel or wrist and some at the spine or hip?
Any bone density test can be useful, but the bone measured and the preferred method depends on how the results of the test are going to be used. Heel or wrist bone density measurements are usually done with special portable machines, and are generally more available and less expensive than spine or hip measurements. Because osteoporosis is usually generalized throughout the skeleton, a simple measurement of bone density in the heel or wrist helps to determine if a person has low bone density relative to what they might have had when they were younger. These methods give a better indication of overall skeletal status in women over age 65 than for women early after menopause. For younger women, a measurement at the spine is the most sensitive way to determine if they have osteoporosis. Also, because the spine changes fastest with therapy or with low estrogen levels, it is usually the best site to measure for women who are starting therapy, or those who might want to delay taking hormone or other therapy until they see how their bones may be changing. Bone density measurements at the hip are most useful in older women and men who may be at higher risk of hip fracture, because a hip measurement gives the best estimate of the risk for hip fracture in these people. If a person is on therapy, however, spine measurements are still more useful than hip or wrist measurements to determine if the therapy is working.
How accurate are bone density tests in determining if I have osteoporosis?
All bone density tests approved by the FDA are considered to give some useful information. A measurement of the spine or the hip is considered the most definitive, and they are mentioned in the Medicare guidelines as the preferred bones to measure. The World Health Organization has also come up with some guidelines for defining who has osteoporosis, based on a bone density measurement. While these guidelines are still being debated, they are one of the best ways we have at this time to determine who may need to be treated for osteoporosis. These guidelines are based on comparing your bone density to the average bone density for young adults, and results are given as a “T-score” (the “T-score” is determined by the range of bone density values in young adults, with 95% of normal young adults having a T-score between -2 and +2). A T-score of -1 or higher is considered “normal” by the WHO guidelines, from -1 to -2.5 is considered “osteopenia,” and below -2.5 is considered “osteoporosis.” It is important to note that these are just guidelines, and that the numbers are intended to be used in the overall evaluation of a patient, and not for a definitive diagnosis, that is, a woman with a T-score of -1.5 who has other risk factors could be considered osteoporotic, while one with a T-score of -2 but no other risk factors might not be a candidate for treatment.
If a bone density measurement in my heel gives a T-score value of -1.5, will this be the same for my spine?
Not necessarily. Measurements made in different bones and with different instruments can give T-score values that differ by as much as 1 or 1.5 units. Most of the time, T-scores that are low for heel or wrist will also be low for spine or hip, but if the heel or wrist is only slightly low, you can still have osteoporosis in the spine. This is especially true in women soon after menopause, because bone is lost faster from the spine than from the wrist, hip, or heel. Because of these differences, many clinicians feel that if the wrist T-score is between -1 and -2, it is important to do a follow-up measurement in the spine or hip to confirm the diagnosis of low bone density. In these cases, Medicare will reimburse both for the initial wrist or heel measurement, and the follow-up spine or hip measurement.
If I start therapy, do I need any special bone density tests?
The Medicare guidelines say that central measurements are the most effective in monitoring bone changes in response to therapy. The two methods used for central bone density measurements are quantitative computed tomography, or QCT, for the spine, and dual energy x-ray absorptiometry (DXA) for the spine or the hip. Because the spine is the first to change, it is the preferred site to measure bone changes, and Medicare guidelines say that measurements every 2 years are allowed for coverage. The guidelines also say that in special cases, more frequent measurements may be covered, for example in patients who are taking high doses of corticosteroids for asthma.
If I am already being treated for osteoporosis or taking hormone replacement therapy, why should I have a bone density test?
Not everyone responds to therapy for osteoporosis in the same way. In the past, only hormone replacement therapy was available for preventing or treating osteoporosis, but some women do not want to take HRT, and in some cases it does not prevent bone loss from occurring even in women taking estrogen. In the past couple of years, new therapies have been approved for osteoporosis. Alendronate (Fosamax) is the first of a class of new drugs called bisphosphonates that can be used to prevent or treat osteoporosis. Selective Estrogen Receptor Modulators (SERMs) is another class of “designer estrogens” that can be used, with raloxifene (Evista) the first of these to be approved. Calcitonin nasal spray is also an approved treatment for osteoporosis. All of these treatments are alternatives to HRT, all are more expensive than HRT, and all have some side effects, so it is important to make sure that they are working to prevent bone loss. Bone density tests, especially at the spine, are the most accurate way to detect if a treatment is preventing bone loss.
Do bone density tests use x-rays?
Almost all bone density tests use small amounts of x-rays to measure the amount of bone. The exception to this are the new ultrasound machines that measure bone at the heel or in the leg, but these are only used for a “peripheral” bone test and are not used to monitor changes in the bone with therapy. The amount of x-rays used by all other bone density tests are less than chest x-rays or dental x-rays, and substantially less than for a mammogram or conventional x-rays of the spine.
Do men get osteoporosis?
Yes. While osteoporosis is often considered a “woman’s disease,” men also get osteoporosis. After age 70 or 75, about one-third of hip fractures are in men. Osteoporosis in men may have some different risk factors than in women, but as men live longer the chances of them having a fracture increase just like for women. There is not as much information about bone density and osteoporosis in men as in women, but most experts consider that bone density measurement in men is useful, especially in those over 65 and with other risk factors.
How do we interpret QCT results?
QCT, like any bone density measurement, is used to compare a patient to normal control data or to an absolute reference value, and to measure the change in bone density with time in a given patient. Researchers have established a “fracture threshold” level for all bone density methods; patients with bone density above this level are rarely seen with osteoporotic fractures, while below it the prevalence of patients with fractures rises. This level is about 100–110 mg/cm3 for QCT. As the value decreases below this the fracture prevalence increases, so that below 50 mg/cm3 most patients seen already have spinal fractures. The QCT value for a patient, when added to other diagnostic information, can be helpful in deciding an approach to treatment. Serial QCT measurements can establish the rate of change of bone mineral density in both treated and untreated patients, but the sensitivity of the method depends on how well the technique is done at a given hospital. In most cases, a change of 8–10 mg/cm3 can be significant or at least indicate a trend, and several serial measurements all changing the same way improve confidence in the result. Women within 1–3 years after menopause average 7 mg/cm3/yr loss, so yearly measurements can be helpful. Bone loss may be slower in older individuals. The frequency for each patient will depend on other diagnostic and treatment factors, and it is important to interpret the bone density results within the context of each individual’s clinical status.