A Dual-Energy X-ray Absorptiometry (DEXA) scan is a non-invasive imaging test that uses a very low dose of radiation to accurately measure bone mineral density, typically in the hip and spine. This procedure is the standard method for diagnosing conditions like osteoporosis and assessing fracture risk. Accurate results depend heavily on specific preparations the patient must follow before the appointment. These steps eliminate outside interference that could skew bone health measurements.
Dietary and Supplement Adjustments
The most important pre-scan adjustment involves temporarily stopping certain supplements. Patients must avoid taking any calcium supplements for at least 24 hours before the scheduled DEXA scan. This rule also applies to multivitamins and calcium-based antacids.
The reason for this temporary cessation is that undissolved calcium from supplements can remain in the gastrointestinal tract during the scan. This residual calcium may be picked up by the DEXA machine’s X-ray beam, artificially inflating the bone mineral density reading. While supplements must be skipped, patients can generally continue to consume foods that naturally contain calcium.
There is generally no strict requirement to fast before a DEXA scan, and patients may eat and drink normally. However, avoid consuming a large, heavy meal in the two to four hours immediately preceding the test. If the scan measures body composition, a large meal can temporarily affect water content and distribution, impacting the precision of the analysis.
Clothing and Personal Item Restrictions
The accuracy of the DEXA scan relies on the unimpeded passage of the X-ray beam through the body. Therefore, patients should wear comfortable, loose-fitting clothing that is entirely free of metal components. Common interfering items include zippers, metal buttons, snaps, buckles, and metallic threads woven into the fabric.
Metal objects create artifacts, or shadows, on the resulting X-ray images. These artifacts can obscure the bones being measured and make the data unreadable or inaccurate. For example, an underwire bra must be avoided, as the metal can interfere with the scan of the spine. If a metal-free outfit is not worn, the patient will be asked to change into a hospital gown.
It is also necessary to remove all jewelry and personal accessories, including necklaces, earrings, watches, and bracelets. Patients should leave all safely removable jewelry and body piercings at home to streamline the check-in process. Removable dental hardware may also need to be taken out before the scan, depending on the area being imaged.
Timing and Prior Procedure Requirements
The timing of your DEXA scan relative to other medical procedures is a significant factor in ensuring result accuracy. Diagnostic tests using contrast agents or radioactive tracers can leave residual material in the body. This residual material interferes with the DEXA machine’s ability to measure bone mineral density correctly, potentially leading to inaccurate readings.
A waiting period is required after procedures involving contrast or nuclear medicine. Patients who have recently undergone a CT scan with intravenous contrast, an MRI with gadolinium, a barium study (like an upper GI series), or a radioisotope scan must generally wait at least 7 to 14 days. The specific waiting time varies based on the type of contrast agent used, so communicate any recent procedures to your provider.
Another safety consideration is the use of X-rays, even though the radiation dose from a DEXA scan is very low. Female patients must inform the technologist if there is any possibility of pregnancy. Due to the use of radiation, the procedure is typically avoided entirely during pregnancy to minimize any risk to the fetus.