The Dual-Energy X-ray Absorptiometry (DEXA) scan is the established method used to measure bone mineral density (BMD). This diagnostic tool is the gold standard for assessing bone health and diagnosing osteoporosis, a condition characterized by low bone mass and increased fracture risk. The DEXA scan passes two different X-ray beams through the body, typically targeting the hip and spine, to determine bone tissue density. Proper preparation, including careful consideration of attire, is necessary to ensure accurate results.
Clothing Guidelines for the DEXA Scan
Whether you can wear a bra during a DEXA scan depends entirely on its construction. Any clothing item containing metal must be avoided, including most standard bras that feature metal underwire or hook-and-eye closures. These metal components, even small ones, can interfere with the low-dose X-ray technology used by the scanner.
This rule extends to all parts of your attire; zippers, snaps, dense plastic embellishments, and metal buttons on shirts or pants should also be avoided. The safest choice is to wear loose-fitting, comfortable athletic wear, such as a metal-free t-shirt and elastic-waist pants or shorts. If you prefer a bra, a soft, wireless sports bra confirmed to be completely free of metal or thick plastic is generally acceptable. Alternatively, most scanning facilities provide a clean, metal-free gown for you to change into before the procedure.
How Metal and Plastic Affect Bone Density Results
The requirement for metal-free clothing stems from the physics of how the DEXA machine measures bone density. The scanner operates by analyzing how much of the two distinct X-ray energy beams are absorbed by the body’s tissues. Bone absorbs the beams differently than soft tissue like fat and muscle, allowing the machine to calculate the BMD.
Dense materials, particularly metal, absorb the X-rays far more intensely than bone or tissue. When a metal object, such as an underwire, lies in the scan field, it creates a bright, unwanted distortion known as an artifact on the resulting image. This artifact blocks the path of the X-ray beams, preventing an accurate measurement of the underlying bone.
The presence of these artifacts can artificially inflate or deflate the calculated bone mineral density, especially in the spine area. Extraneous metal can skew bone mineral content results by a significant percentage, potentially leading to an inaccurate T-score or Z-score. An incorrect score could result in a misdiagnosis of osteoporosis or mask a true change in bone health, compromising treatment decisions.
Essential Preparation Steps Beyond Clothing
Beyond removing all metal and wearing appropriate attire, several other preparation steps are essential. Avoid taking any calcium supplements or multivitamins for at least 24 hours before your scheduled scan. Recently ingested, unabsorbed calcium in the gastrointestinal tract can mimic bone density, leading to a falsely elevated BMD reading.
You must inform the technician if you have recently undergone any X-ray procedures that used a contrast agent (e.g., a barium study or an intravenous pyelogram). These contrast materials can remain in the body and interfere with the DEXA scan, requiring a waiting period before the test can be performed. Any pre-existing metal implants in the scan area, like a hip replacement or spinal hardware, must also be communicated to the technologist so they can be excluded from the measurement analysis. Women who are pregnant or suspect they might be pregnant should notify their provider immediately, as DEXA scans use a small amount of radiation and are generally avoided.