Dual X-ray Densitometry (DEXA), the most advanced and reliable method to screen for osteoporosis quickly and painlessly, is available in the office.

DEXA scans are very accurate in assessing a patient's bone fracture risk and need for treatment. The DEXA scan is more sensitive than ordinary X-rays in diagnosing bone loss at an early stage. Safe and painless, the 15-minute DEXA scan is the most reliable test to determine even the earliest stages of bone loss associated with osteoporosis. It is also used in determining a person's risk for hip fractures. The DEXA scan is like an X-ray, except it uses less radiation—only about 20 percent of a standard chest X-ray.

Osteoporosis is a condition of low bone mineral density that causes loss of bone strength. This can lead to deformities, bone pain and fractures. Until recently, doctors couldn't diagnosis patients with osteoporosis until a bone fracture occurred. DEXA scanning has emerged as the preferred imaging technique to diagnose and monitor osteoporosis. It is also used for scanning for early stages of low bone density, even before symptoms occur. In performing a bone mineral density assessment, DEXA:

• detects the presence of osteoporosis in men and women with particular risk factors;
• screens for osteoporosis;
• predicts future fracture risk; and
• monitors bone density in those with low normal levels and in those with osteoporosis who are undergoing treatment

With the information from the DEXA scan, the doctor can start and monitor treatment if needed.

There are a number of other ways for calculating bone density or bone turnover. These are generally not as satisfactory as DEXA scanning. DEXA scanning is often performed in an office or outpatient facility. The procedure does not require the patient to be in any kind of “tube.” There are no injections, contrast dyes or medications of any sort necessary to do the examination. The amount of radiation is very low, so people with pacemakers, artificial joints or metal inside the body can safely have a DEXA scan.

How does DEXA work?
The DEXA scan is more accurate and precise in measuring bone mineral density. The bone area is scanned at a set frequency with X-ray energy alternating from two different sources. The two sources of X-ray energy are then filtered through a counter. The counter reads the amount of bone mass present by selectively subtracting the higher energy image from the lower energy image.

With the patient lying on his or her back, a small arm passes over the body, about two feet above the stomach and hips, scanning the bone density at the hips and spine. (The hips and spine are measured because that is where osteoporotic fractures occur most often.) A technologist sits next to the examination table to monitor the procedure from a computer, and a medical radiologist reads the results.

How is bone density measured?
A DEXA scan report compares the patient’s bone mineral density values with that of a normal young patient (T score) and a normal age-matched patient (Z score). Comparing bone density against peers aids in determining if the patient’s bone density is exceptionally low.

The table below compares the T score or Z score to an equivalent percentile. For example, if the patient was pre-menopausal, and the T score was 0.0, half of the pre-menopausal population has greater bone density, and half less. If the score were -1.0, there would be 84% with greater bone density.

Fortunately, there are tables that allow an easy conversion of standard deviations to percentages. For example, a Z-Score of -1.8 means that patients at the 4th percentile, or 96% of women in that category, have greater bone density than the patient. A T-Score of -2.0 means a patient at the 2nd percentile, or 98% of pre-menopausal women have greater bone density than the patient. A T-score between -1 and -2 represents significant bone loss or osteopenia. The World Health Organization considers a T-Score of -2.5 or below to signify osteoporosis. And many U.S. organizations deem -2.0 or below to represent osteoporosis.

NOTE: Lead aprons or other protective garments are unnecessary, as the amount of radiation is so low that the garments are deemed excessive. As with any medical procedure, if you are pregnant or trying to become pregnant, you should not have this scan.

WHAT IS A BONE MINERAL DENSITY (BMD) TEST?
Following a comprehensive medical assessment, your doctor may recommend that you have your bone mass measured. Bone mineral density (BMD) test measure bone density in the spine, hip, and/or forearm. These are the most common sites of fractures due to osteoporosis, a disorder in which bones gradually become thinner and weaker. Osteoporosis is often called the "silent killer" because the condition can often go undetected until it is severe and fractures begin to occur. Until the age of about 30, you build and store bone efficiently. Then, as part of the natural aging process, your bones begin to break down faster than new bone can be formed.

RISK FACTORS FOR OSTEOPOROSIS

• Being female
• Being thin and/or having a small frame
• Advanced age
• A family history of osteoporosis
• Estrogen deficiency as a result of menopause, especially early or surgically induced
• Anorexia nervosa
• Low lifetime calcium intake Use of certain medications, such as corticosteroids and anitconvulsants
• Low testosterone levels in men
• An inactive lifestyle
• Current cigarette smoking
• Excessive use of alcohol
• Being Caucasian or Asian, although African Americans and Hispanic Americans are at significant risk as well

WHY WOULD I NEED A BMD TEST?
A bone density test can:

• Detect osteoporosis before a fracture occurs
• Predict your chances of fracturing in the future
• Confirm a diagnosis of osteoporosis if you have already suffered a fracture.
• Determine your rate of bone loss and/or monitor the effects of treatment if the test is conducted at intervals of a year or more

HOW IS BONE DENSITY MEASURED?
Bone density is measured through painless, noninvasive scanning techniques based on X-ray radiation. These techniques require you to be positioned for the scan and hold still while it is being completed. Dual Energy X-ray Absorptiometry (DEXA) measures the spine, hip, and/or forearm, and is the most widely used technique available. The procedure exposes the patient to little radiation, needs little scanning time, is inexpensive and is highly accurate. Because of its precision, DEXA is well suited to making serial (repeated) measurements. Serial bone density measurements may be done to track bone loss over time, to evaluate the effectiveness of treatment, or as part of a clinical trial for a new potential treatment for osteoporosis.

HOW DO I PREPARE FOR AN EXAM?
Wear comfortable clothing with no metal zippers, buttons, or buckles. Let the technologist know if you are pregnant or think you may be. Also let the technologist know if you have had recent fractures, metal implants inside your body (hip replacements or back surgeries). It is also important to inform the technologist if you have had a recent nuclear medicine scan or a barium exam.

WHAT CAN I EXPECT DURING MY EXAM?
During a DEXA bone density scan, you will be asked to lie on a table on your back. The scanner arm will move back and forth over the part of your body being scanned. Typical DEXA exams are completely painless and only take 10-15 minutes to perform.

WHAT DO THE RESULTS MEAN?
Your bone density is compared to two standards, or norms, known as "age matched" and "young normal." The age-matched reading compares your bone density to what is expected in someone of your age, sex, and size. The young normal reading compares your density to the optimal peak bone density of a healthy young adult of the same sex. The information from a bone density test enables your doctor to identify where you stand within ranges of normal and to determine whether you are at risk for fractures. In general, the lower your bone density, the higher your risk for fractures. Test results will help you and your doctor decide the best course of action for your bone health.

DEXA (Dual Energy X-ray Absorptiometry) is the most widely available method of bone densitometry, and most insurance plans will cover the cost for the test, given that certain medical indicators are present. Bone mineral density measurement with DEXA is painless, and requires no injections, invasive procedures, sedation, special diet or any other advance preparation. During a DEXA exam, the patient lies fully clothed on a padded table while the system scans one or more areas of bone (usually the lower spine or hip). The entire exam typically takes just a few minutes to complete. While DEXA uses x-rays, the radiation dose is less than during a chest x-ray. Each patient's bone density is plotted against the "normal" for a healthy young adult or against age matched control data. A radiologist or other physician then interprets the data and creates a concise report on the status of the patient's bone density.

Laboratory tests that measure the amount of collagen in urine samples can indicate bone loss. Lab tests may also be used in conjunction with DEXA or other methods of bone densitometry to diagnose osteoporosis.

New methods of measuring osteoporosis using ultrasound have also been developed. One such ultrasound system measures BMD at the patient's heel and takes about a minute. The ultrasound systems for testing osteoporosis are smaller and less expensive than traditional DEXA systems. These systems have recently received US Food and Drug Administration (FDA) clearance. The hope is that this more compact, lower cost system will allow this vital diagnostic test to become more widely available in the future. By primarily measuring peripheral sites such as the heel, ultrasound densitometry may not be as sensitive as techniques such as DEXA or QCT that measure the spine or hip since the heel may be normal in bone density even when central sites such as the hip or spine are already significantly abnormal.

Further, density changes in the heel occur much slower than in the hip or spine. Therefore ultrasound densitometry should not be used to monitor a patient's response to therapy. However, the new ultrasound densitometry systems will allow many more people access to bone densitometry and potentially diagnose osteoporosis before a traumatic fracture occurs.

Summary of Types of Bone Mineral Density Tests

• Ultrasound measures the heel
• DEXA (Dual Energy X-ray Absorptiometry) measures the spine, hip or total body
• SXA (single Energy X-ray Absorptiometry) measures the wrist or heel
• PDXA (Peripheral Dual Energy X-ray Absorptiometry) measures the wrist, heel or finger
• RA (Radiographic Absorptiometry) uses an X-ray of the hand and a small metal wedge to calculate bone density
• DPA (Dual Photon Absorptiometry) measures the spine, hip or total body SPA (Single Photon Absorptiometry) measures the wrist
• QCT (Quantitative Computed Tomography) measures spine or hip

The accuracy of bone mineral density test is high, ranging from 85% to 99%. According to physicians, QCT is the most accurate BMD test and ultrasound is the least accurate of the tests. DEXA is the most widely available BMD test and its accuracy is in between those of QCT and ultrasound. However, QCT is not widely available and delivers more radiation to the patient than DEXA.

Patients Recommended for Bone Mineral Density Measurements:

• Post-menopausal women with at least one additional risk factor (other than menopause).
• All women older than 65 regardless of risk factors.
• Post-menopausal women who present with fractures.
• Women considering therapy for osteoporosis, if bone mineral density (BMD) testing would affect the decision.
• Women who have been on hormone replacement therapy (HRT) for prolonged periods of time.

Medicare Guidelines for Bone Densitometry:

• Estrogen deficient women at clinical risk for osteoporosis.
• Individuals with vertebral abnormalities.
• Individuals receiving, or planning to receive, long-term glucocorticoids.
• Individuals with primary hyperparathyroidism.
• Individuals being monitored to assess the response of efficacy of an approved osteoporosis drug therapy.

• Medicare will only reimburse when BMD tests are ordered by the treating health care provider.
• Frequency of BMD testing is once per two years.
• Benefit applies to all Medicare patients including managed care programs.
• Non-Medicare payers may have different guidelines.

Understanding the Results of Bone Mineral Density Tests: T-score and Z-score
Bone mineral density (BMD) tests are performed to determine whether a patient has osteoporosis or osteopenia, a low bone mass that puts her at risk for osteoporosis. To make this determination, the technologist will calculate the patient's T-score.The World Health Organization (WHO) established the criteria for determining the T-score.

To calculate a patient's T-score, physicians subtract the patient's measured BMD from a BMD reference range of women in their thirties (YN = young normal). Around age 35, bone mass is usually at its peak and fracture risk is at its lowest. This figure is then divided by the standard deviation (SD).

T Score = (BMD - YN) / SD

By determining a patient's T-score, the physician will see whether a woman has or is at risk for osteoporosis:

As a rule, a patient's fracture risk doubles for every SD (standard deviation) below the young adult reference range. For example, if a patients' T-score is -2 SD, she is at four times greater risk of a fracture than a young woman at peak bone density.

Physicians may also measure a patient's Z-score with a bone mineral density test. The Z-score compares the patient's measured BMD to the average BMD measurement for the patient's age and sex. The Z-score is not used to confirm a diagnosis of osteoporosis because a favorable BMD measurement (compared to the average BMD measurement for the patient's age group) does not mean the patient is not at risk for osteoporosis.

Bone mineral density increases until around age 35 and then levels off until menopause. During the first six to eight years of menopause, there is a sharp decline in bone mineral density. It is estimated that between 1% and 5% of bone density is lost at this time. The higher a woman's overall bone density, the less she will be affected when she loses bone density at menopause.