Why measure bone mineral density?
At least 30 to 40 percent of bone mineral must be lost before bone loss is detectable on a routine X-ray, and that is too late for an effective prevention of fracture risk. Specialized tests have been developed to detect small amounts of bone mineral loss in those people at risk. The most widely available and preferred technique is Dual-Energy X-ray Absorptiometry or DXA.
How is bone mineral density measured?
During the DXA examination, the patient lies on a padded table while a “scanning post” passes back and forth over the site of the skeleton being measured. No injections or dyes are used. A simple and fast procedure, the DXA is a comfortable diagnostic test that measures bone mass in the spine, hip and forearm.
During a five- to seven-minute period of time, an X-ray beam records the amount of calcium in the skeleton. The DXA machine’s computer, then, calculates the amount of bone mineral and compares it to values considered normal for persons of the same gender as the patient.
The amount of X-ray received is minimal — only one-sixth that of a chest X-ray or what a person might be exposed to from the altitude while flying from New York to Los Angeles. Even though the X-ray exposure is minimal, DXA of the hip and spine is not performed on pregnant women as a matter of institutional health policy. Bone mineral density measurements of the forearm may be used in pregnant women.
A trained Bone Density Technologist certified by the International Society for Clinical Densitometry (ISCD) performs the DXA scan. He or she will explain the procedure to you. The specialist physicians at the Bone Health Program, most of whom are ISCD Certified Clinical Densitometrists, will interpret the results and discuss it with you at the visit, in most cases immediately after the test. The physician will also submit a report including detailed measurement data to your physician within a few days.
What is the benefit of the test?
The DXA provides a safe, inexpensive and accurate means of measuring bone mineral density. Similar to a baseline mammogram, the initial DXA provides a baseline measurement or point of comparison for future measurements. Repeated measurements at specified intervals determine an accurate rate at which bone is being lost and provide a means to monitor the effectiveness of treatment.
The DXA measurement helps physicians assess the likelihood of developing fractures that may occur during normal living activities, or after minimal trauma. For example, more than 30 percent loss of bone mass in the hip leads to a significant increase in the fracture rate.
Under the aegis of the World Health Organization, a tool has been developed, the FRAX calculator that aids in estimating fracture risk based on bone density but also taking into account other factors that are known to increase fracture risk, such as family history of osteoporosis, having had a previous low-trauma fracture, taking medications that negatively affect bone strength (i.e. corticosteroids for rheumatoid arthritis, lupus, or asthma), smoking, and others. While this tool is freely available online, we strongly encourage you to consult with your specialist physician or health care provider to devise the most appropriate approach to improve and maintain your bone health.
How can a DXA test be scheduled?
Making an appointment is easy, please call 314-454-7775. Appointments can be scheduled usually within two weeks. During the first phone call, you will be asked the name of your referring physician, and other basic information about yourself. If you need a referral from your insurance company, please obtain authorization before your appointment.
What should patients do to prepare for this test?
You do not have to prepare anything special for the DXA. Keep to your normal diet and daily routine. The whole DXA takes 20 minutes from start to finish, including filling out any of the other required forms. To help with the paperwork, you can download and fill out a simple Patient Questionnaire (pdf) and Medication Record (pdf).
To make the examination easier, we recommend that patients wear loose fitting comfortable clothing, such as sweatshirts and sweat pants with no zippers, buttons, or safety pins, or other metal fasteners. Patients may be asked to change into a hospital gown. Also, please do not take calcium supplement tablets the day of the test, since if not completely dissolved in the stomach, it may interfere with a proper estimation of bone density.
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