A bone density test, formally known as Dual-Energy X-ray Absorptiometry (DEXA or DXA), is a non-invasive imaging procedure that uses low-dose X-rays to measure bone mineral density (BMD) in specific areas of the body, typically the hip and spine. The primary purpose of this test is to assess bone strength and determine a person’s risk for fractures, often used in the diagnosis of osteoporosis. Proper preparation is necessary because certain substances and recent medical procedures can interfere with how the X-rays are absorbed and measured. Following specific guidelines ensures the reading accurately reflects your true bone health.
Immediate Preparation Guidelines
Strict fasting is not required before a DEXA scan, and you can generally eat and drink normally. However, avoid consuming an unusually large meal right before the test, as this could potentially influence the measurement. The most important immediate restriction involves supplements containing calcium, which must be temporarily avoided.
You must refrain from taking calcium supplements, multivitamins that contain calcium, or antacid tablets like Tums for at least 24 hours prior to your appointment. These products can linger in the gastrointestinal tract and appear on the scan, artificially inflating the bone mineral density reading and leading to inaccurate results. Routine medications that do not contain calcium can usually be taken as scheduled, but always confirm this with the testing facility or your healthcare provider.
On the day of the test, wear loose, comfortable clothing without any metal components. Physical metal, such as zippers, buttons, buckles, or underwire, interferes with the X-ray beam and creates artifacts on the image. You will also be asked to remove all jewelry, including piercings, watches, and other metallic accessories before the scan begins.
Long-Term Medication and Supplement Considerations
Preparation extends beyond the immediate 24-hour window, especially regarding recent diagnostic imaging procedures. Certain medical tests use contrast agents that can remain in the body for days or weeks and interfere with the bone density measurement. If you have recently undergone a Barium study or a procedure requiring injected contrast dye for a CT or MRI scan, the DEXA scan must be postponed.
The residue from these contrast materials absorbs the X-rays, leading to a falsely elevated bone density reading. Providers advise waiting a minimum of seven to 14 days following any procedure involving contrast agents to allow the material to fully clear from your system. Inform the technologist about any such recent procedures when scheduling your DEXA appointment to prevent rescheduling.
Discuss any long-term osteoporosis medications you are currently taking with your physician or the testing facility. Depending on the specific drug and the purpose of the scan, some facilities may advise continuing these medications while others may recommend temporarily holding them. Open communication about all recent and long-term medical treatments is necessary to secure the most reliable data from the DEXA scan.
What to Expect During the Test
The DEXA scan is a non-invasive procedure that usually takes between 10 and 20 minutes to complete. You will be asked to lie still on your back on a padded table. A technologist will assist you with positioning your limbs, often using a foam block to elevate your legs for the hip and spine measurements.
A mechanical arm, called the C-arm, slowly passes over the area being scanned, emitting a narrow beam of low-dose X-rays. The radiation exposure is minimal. Remaining completely motionless throughout the scan is important, as any movement can blur the image and necessitate a repeat of the segment.
After the scan is finished, there is no recovery time needed, and you are free to resume all normal activities immediately. The images are then analyzed by a radiologist or physician, who interprets the bone density data to generate a T-score and Z-score used to assess bone health. The final results are typically sent to your ordering physician within a few working days.