Bone Mineral Density Exams
What is a DEXA Bone Density Scan?
Dual Energy X-Ray Absorptiometry, called DEXA is a scientific way of measuring your bone density. Low dose x-ray is used from different angles projected at bones in the spine, hip, or wrist to determine the density or mass of the bone. Other names for this test are Bone Mineral Density (BMD) or Dual X-ray absorptiometry (DXA). The dose of the x-ray is so minimal that the technologist sits next to you during the entire exam.
Why is Bone Density Important?
Our peak bone mass is usually achieved in young adults between 21-24. This peak density varies between women and men, and among different ethnicities. This peak density is assumed for you by comparing your density to a large database of women (or men) of similar height, weight, and ethnic groups. There are different database references for caucasian women compared to African American men.
What Conditions Affect Bone Density?
Our genetics, diet, and sex hormones allow us to achieve a maximum density in our mid-twenties. After that time, the density typically decreases slightly over time. The greatest changes in density are noted in women after menopause when hormones are much lower. Men also exhibit the greatest decrease in density after age 50 when the sex hormones (testosterone) fall precipitously.
Our diet and nutritional access play a significant role in the development of peak bone density and the maintenance of normal bone mass. A diet rich in calcium is essential at all age levels. Foods that are rich in calcium include milk products, most vegetables, and most supplemented foods. The average American has adequate calcium intake during most of our lives until we become older. Meeting adequate dietary calcium intake in the elderly may become problematic for several reasons. As we age, we lose our sense of taste, and other medical problems or medication may make it harder to maintain adequate intake. Therefore, many patients who struggle with this will be asked to supplement with over-the-counter calcium.
We don’t make our own active Vitamin 3. Therefore, we can either have sufficient sun exposure to allow our skin to convert the inactive to the active form or we can consume supplemental vitamin D 3. Vitamin D 3 levels are not typically tested but in some conditions may be necessary such as underlying renal, liver, small bowel absorption problems, or thyroid conditions.
How Does Family History Influence My Future Fracture Risk?
We know that family history is a significant risk factor for osteoporosis. If your first-degree relatives had been diagnosed with osteoporosis, you may be at risk. Peak bone density is strongly influenced by hereditary factors. Your body weight and height affect the stimulation of bone cortical thickening. A thicker bone cortex is necessary to hold a heavier frame. On the other hand, low body weight is a significant risk factor for low bone density. A loss of height of greater than 1⁄2 inch over one year interval is also considered a risk factor.
Do Prior Fractures Affect My Density?
Your history of prior fractures may influence your future risk for fracture. It depends on the circumstances that caused the fracture in the first place. If a person with the same build and ethnicity as you would not have fractured, then your insufficiency fracture is significant. If, on the other hand, you were involved in a traumatic injury such as a car accident, then this history should not be used to predict your future risk.
What Other Factors Affect My Bone Density?
Some medicines such as corticosteroids, overtreatment with thyroid supplements, smoking, and excess alcohol consumption affect bone density. Many medical conditions affect bone density including liver, kidney disease, small bowel absorption issues or celiac disease, autoimmune conditions such as rheumatoid arthritis, hyperthyroidism, hyperparathyroidism, among others.
When to Start Bone Density Scan?
The International Society of Bone Densitometry (ISCD) and the National Osteoporosis Foundation (NOF) recommends bone density scans to start by age 65 for most women and 70 for most men of average risk. Since most women become menopausal after age 50, a woman who does not take hormone replacement therapy and who has a family history of osteoporosis may be screened for low bone density using menopausal and family history risk factors. A woman who goes onto hormone replacement and does not have any family history or other significant risk factors may wait until age 65 if her clinician advises.
How Do I Prepare For My DEXA Scan?
Do not take calcium tablets or other large mineral tablets as the tablets may still be in the bowel and overlap on images of the spine. Avoid wearing clothes with metal buttons or naval jewelry. A two-piece outfit with an elastic band is optimal.
How is a Bone Density Scan Performed?
You will lie comfortably on a soft paddled table starting on your back. The technologic will position you appropriately in the middle of the beam. The x-ray tube moves slowly across your spine. Another scanning device in the table called a photo generator passes beneath you. This is where the name “Dual Energy” in the name DEXA comes from. After that image is acquired, you will be positioned on your side to obtain the Lateral Vertebral Assessment (LVA). The hip density is assumed to be the same using either
side so historically, the left hip is typically selected to measure the density. If there is a reason that your hip densities would not be symmetrical such as one leg much shorter than the other, then let the technologist so that she can measure both hips. IF you have had a hip joint replacement, we can scan the opposite hip. If both hips have been replaced, then we can omit that score and select the forearm instead. If you have an underlying medical problem with your serum calcium or hyperparathyroidism, then scanning your forearm is performed.
If you have any medical reasons why you cannot assume these positions, please let our technologists know in advance so we can alter the examination.
What DoThe Scores Mean?
A T-Score of -1.0 or higher is normal
T-score -1.0 to -2.5 is low bone density (osteopenia) T-score -2.5 of greater (more negative) is osteoporosis
How Can I Treat Osteopenia or Osteoporosis?
At a very minimum, increase your weight-bearing or resistive exercises. Not all exercise is capable of achieving this. Walking up a hill carrying a backpack will improve bone density while biking will decrease your density. Biking is not resistive-you are using a machine to decrease your work and the muscles are not resisting a force. Also, Take sufficient Vitamin D3. For most healthy adults, taking 1,000 IU/day is sufficient but some people may need to take more. If there is a medical reason why you may not be able to absorb Vitamin D appropriately (like with celiac disease) or convert it to its active form (liver disease), you may want to have a Vit D3 level measured.
Many medications have been developed that improve bone density by either reversing the proportion of bone turnover or by anabolic building new bone (PTH). Bone is a dynamic organ-it is continually being built up by osteoblasts or being broken down (called remodeling) by osteoclasts. The balance of building and breaking down is normal. Specialists discovered that by slowing the caustic activity, the blastic activity naturally wins over and increases bone density. Medicines called bisphosphonates like Fosamax and Actonel are typically first-line oral medications used to treat low bone mass. Other medicines like Boniva can be given as a pill or IV infusion quarterly. Prolia can be used in people with decreased kidney function or in patients who can’t take oral medications easily. Reclast is given by IV infusion once yearly. Other anabolic medicines help “build new bone” like Forteo.