Osteoporosis Screening: What You Need to Know

As older adults face pressure from their doctors to be tested (and then possibly treated) for osteoporosis, it is important that they understand the tools used to determine their diagnosis. The development of new screening tools for osteoporosis has been helpful in estimating the 10-year risk of a hip or any osteoporotic fracture, but these tests still omit several important risk factors in their calculation and have the potential for resulting in inappropriate drug treatment for people who may not necessarily need it.

Osteoporosis is usually diagnosed in one of two ways. First, the patient can have a low Bone Mineral Density (BMD) score, represented by a so-called “T-score” less than -2.5. BMD is most commonly measured by dual-emission X-ray absorptiometry (DXA). The T-score represents the number of standard deviations (a representation of the distribution of BMD values in the population) from the average BMD of a young woman; negative T-scores represent lower BMDs than average.

The second way osteoporosis may be diagnosed is after a fragility fracture. A fragility fracture occurs when a bone breaks under a force that would not break a healthy bone, such as falling down from a standing position.

BMD peaks in the 20s and thereafter begins to decline. In women, BMD begins to decline more rapidly after menopause; this is thought to be due to loss of estrogen production by the ovaries. In order to detect women at risk for fracture, the U.S. Preventive Services Task Force recommends that all women over 65 years old (and some women 60-64 years old with risk factors mentioned in Box 1 ) be screened for low BMD. Screening for low BMD before 65 years of age is controversial and guidelines are vague. Nonetheless, screening occurs for many women at some point between menopause and 65 years of age.

Screening for low BMD with DXA is intended to identify patients at risk for fractures so that they might be referred for treatment to prevent fractures. But, much like measuring blood pressure or cholesterol to screen for stroke or heart disease, BMD is only one aspect of the disorder; microscopic bone architecture and the likelihood of falling are crucial aspects of fracture risk, yet neither is reflected in a BMD value. While women with a low BMD are at increased risk for fractures, low BMD (T-score less than -2.5) does not adequately identify most women who will go on to develop a fracture. Only 25 to 45 percent of women who sustain a fracture have T-scores less than -2.5. Additionally, in the same patient, the T-score varies depending on what part of the skeleton is measured.

Because almost 50 percent of fragility fractures occur in patients with T-scores between -1.0 and -2.5, a condition known as “osteopenia,” the focus is shifting toward recognizing risk factors for fractures other than low BMD (see Box 1 ). In consultation with a physician, these factors may be used to decide whether screening for low BMD is necessary.

New diagnostic tools not requiring BMD: helpful but incomplete

To address the deficiencies in using BMD alone in determining fracture risk, the World Health Organization recently released an online tool called FRAX (available at http://www.shef.ac.uk/FRAX/ ). FRAX can estimate one’s 10-year risk of hip or any osteoporotic fracture based on risk factors (such as gender, smoker status and daily alcohol consumption), and can be run with or without the results from testing for BMD.

A similar tool developed at the University of Washington (available at http://courses.washington.edu/bonephys/FxRiskCalculator.html) uses elements of FRAX combined with several other factors (for instance, do you use your arms to stand from a chair?) to provide a more detailed and technical assessment of fracture risk, but, unlike the WHO calculator, this tool requires knowledge of one’s T-score.

However, despite the usefulness of these tools, several important aspects of fracture risk are left out. For instance, exercise substantially increases BMD and reduces the likelihood of falling, yet physical activity is not accounted for in either online assessment. Falling is the antecedent to most hip fractures; however, several important determinants of one’s risk of falling were not included in FRAX (see Box 2 ).

Below, we illustrate how these tools can be used and how, surprisingly often, a BMD measurement alone would not lead to a change in treatment. The examples use the FRAX tool and are based on the assumption that only those with a risk of a hip fracture of 3 percent or greater in the next 10 years should begin treatment with medication.

Low-risk patient. Using FRAX without any BMD data, a 55-yearold white female who is five feet four inches tall and weighs 169 pounds with no risk factors has only a 0.4 percent chance of fracturing her hip in the next 10 years (before she is 65 years old). This less than 1 percent risk is obviously much less than the 3 percent risk of hip fracture that might indicate the need for medication. The same lower-than-3 percent risk would also be true for women 60 or 70 years old of the same height and weight with no risk factors.

Using FRAX with BMD information, even if the 55-year-old woman had a T-score equal to -2.5 (osteoporosis), her 10-year hip fracture risk is still only 2.6 percent. Thus, with or without the BMD results, this patient would not be a candidate for treatment.

Intermediate-risk patient. If the 55-year-old woman in the first case was a smoker and had a previous fragility fracture, without knowing her T-score, her risk of hip fracture before 65 years is 2.2 percent. However, with a T-score of -2.5, her hip fracture risk would rise dramatically to about 9 percent. For this patient, assessing BMD could lead to her being treated.

High-risk patient. If, in addition to smoking and a previous fracture, the patient drinks three alcoholic beverages per day and is on steroids for rheumatoid arthritis, even without a BMD, her 10-year fracture risk is 12 percent, high enough to merit treatment. Screening for low BMD would not alter her treatment.

In sum, while measuring BMD can be a useful diagnostic test, all too often, its deficiencies are overlooked. Consequently, far more women receive the test than are likely to benefit from it and may well be started on drug treatment based only on the results. No doubt one of the reasons for the heavy emphasis on BMD is the large industry it supports: the companies who make the equipment and the doctors who profit from doing the tests. Most of the other risk factors can be determined in the course of a routine doctor visit, but screening for low BMD requires a diagnostic test that can be reimbursed. We can achieve better application of our limited resources with a more thoughtful approach that stratifies patients according to the many risk factors that contribute to fracture, rather than relying so heavily on primarily screening for low BMD.