Osteoporosis is a condition characterized by thinning and weakening of the bones. It initially has no symptoms, but it can lead to more easily broken bones, especially painful and debilitating fractures of the hips, wrists, and spine.

A bone mineral density test (BMD), which measures the strength of the bone, is used to screen for thinning bones and determine if osteoporosis is present. Initial screening is recommended for women at age 65 and men at age 70. The test results are reported as T-scores which compare the patient's bone density with that of healthy young women. A T-score of -1.0 or higher is normal. A T-score between -1 and -2.49 indicates osteopenia (early thinning of bones.) and is graded as mild, moderate and advanced). T-scores of -2.5 or more indicate osteoporosis.

Clinicians may elect to increase the frequency of screenings if there are additional risk factors that would suggest a faster progression of bone loss such as decreased activity or mobility, or significant weight loss.

Younger men and women may be tested if they have certain risk factors which include a fragility fracture, some chronic diseases such as rheumatoid arthritis and kidney disease, premature menopause, hormone treatment for prostate and breast cancers, significant loss of height, smoking history, family history of osteoporosis, regular use of corticosteroids, significant alcohol use.

But there has been no consensus about how frequently BMD screenings are needed in order not to miss opportunities to prevent fractures. Some providers recommend repeat screenings every 1-2 years. A recent study, published in the New England Journal of Medicine, investigated this issue.

The study followed almost 5000 women for 15 years to determine how rapidly women with normal BMD or with osteopenia progressed to a stage where treatment to prevent fractures was indicated. They researchers wanted to determine how the BMD testing interval related to the timing of the transition from normal BMD or osteopenia to the development of osteoporosis before a hip or clinical vertebral fractures occurs.

The study looked at 4967 women who were 67 years or older and who did not have osteoporosis at the start. Some of the women had normal bone densities and some had mild, moderate, or advanced osteopenia. They followed them for 15 years to determine how long it took each group to get to the point where they developed osteoporosis significant enough to be at enough risk for bone fracture that they would warrant treatment for osteoporosis.

The investigators reasoned that information about the pace or progression of the stages of normal or early bone thinning to clinically significant osteoporosis could help inform decisions about the appropriate intervals for retesting patients.

Based on the rates of transition from osteopenia to osteoporosis in the four groups, normal BMD, mild, moderate, or severe osteopenia, the researchers recommended that women whose initial tests show normal BMD or mild osteopenia can wait 15 years for follow up. Those with moderate osteopenia can wait five years, and those with advanced osteopenia should wait only one year between tests.

The researchers found that the women with the least osteopenia at the outset of the study took the longest to progress to clinically significant osteoporosis. They also found that within each category of osteopenia, the younger women progressed more slowly to osteoporosis than the older women. The transition time to osteoporosis was longer for women who were taking estrogen at the start of the study as compared with women who had taken estrogen before the study began or had never taken it at all.

The researchers maintain that the baseline T-score is the most important factor to consider when choosing how frequently to repeat the BMD test. But they note there may be compelling reasons to screen more often. Clinicians may elect to increase the frequency of screenings if there are additional risk factors that would suggest a faster progression of bone loss such as decreased activity or mobility, or significant weight loss.

They also note that the expected time to osteoporosis is less in the very elderly and that screening every three years instead of every 5 years might be considered for women who are older than 85 years and have moderate osteopenia.

Additionally, the researchers note that their study population was limited to women 67 years of older, 99% of whom were white. The study suggests that different results may have been obtained from analyses that include younger post-menopausal women or men.

Patients may wish to discuss their BMD results and screening recommendations with their physicians. Although this study offers some important new insights, patient care decisions must take multiple factors into account including each patient's unique medical history.