Underwire Bras Can Artificially Increase Bone Density Measurements
Underwire bras should be removed before DXA scanning because metal components can artificially elevate bone mineral density scores, leading to falsely reassuring results that may mask true osteoporosis.
The Measurement Artifact Problem
DXA (dual-energy x-ray absorptiometry) uses X-ray beams to measure bone density, and any material that absorbs or reflects radiation can interfere with accurate measurements. Research directly examining textile effects on DXA found that fabrics with metal components, including those with underwire or metallic thread, significantly alter both bone density and body composition measurements 1.
Specific Effects Documented
The study testing various textiles on DXA phantoms demonstrated:
- Fabrics with reflective material increased measured bone mineral density by 0.008 g/cm² at the lumbar spine
- Total body bone mineral content increased by 3.6 g with certain fabrics
- These changes represent approximately 25% of the least significant change - a clinically meaningful alteration 1
Clinical Implications
This artifact creates a false elevation in bone density scores, which means:
- A patient with true osteoporosis (T-score ≤ -2.5) might appear to have osteopenia (T-score between -1.0 and -2.5)
- A patient with osteopenia might appear to have normal bone density (T-score ≥ -1.0)
- Treatment decisions based on these falsely elevated scores could result in undertreatment of actual osteoporosis, increasing fracture risk and associated morbidity and mortality
Best Practice Recommendations
According to current DXA best practices 2, 3:
Patients should wear:
- Lightweight clothing without metal fasteners, zippers, or buttons
- No underwire bras
- No clothing with reflective material or metallic embellishments
- Ideally, a hospital gown to eliminate all potential artifacts
Dense textiles to avoid include:
- Wool
- Denim
- Clothing with reflective strips or metallic thread
- Any garment with metal components 1
Critical Pitfall to Avoid
The common assumption that "clothing without obvious metal is fine" is incorrect. Even small amounts of reflective material or dense synthetic fabrics can alter measurements enough to change clinical classification and treatment decisions 1. This is particularly problematic because the artifact increases (not decreases) measured bone density, creating false reassurance about bone health.
Given that osteoporotic fractures are associated with significant morbidity and mortality, and that most individuals experiencing fragility fractures do not receive appropriate treatment 2, ensuring accurate initial DXA measurements is critical for proper risk stratification and treatment decisions.