A Dual-energy X-ray Absorptiometry, or DEXA scan, is a medical procedure used to assess bone health. Patients scheduled for this scan are advised to avoid calcium supplements beforehand, which can seem counterintuitive given calcium’s role in bone strength. This guidance is important for ensuring accurate scan results, which directly impact diagnosis and treatment plans.
Understanding DEXA Scans
DEXA scans measure bone mineral density (BMD), a key indicator for diagnosing osteoporosis and assessing fracture risk. The procedure uses a small dose of ionizing radiation, with two distinct low-dose X-ray beams, to differentiate bone, fat, and muscle tissue. One X-ray energy peak is absorbed by soft tissue, while the other is absorbed by bone, allowing software to calculate BMD.
The scan is commonly performed on the lower spine and hips, areas frequently affected by bone loss and prone to fractures. DEXA is a quick, non-invasive method and the standard for measuring BMD. Results are often expressed as a T-score, comparing bone density to that of a healthy young adult.
How Calcium Affects DEXA Results
Calcium supplements, particularly in tablet form, can interfere with DEXA scan accuracy. When ingested shortly before a scan, these supplements may not fully dissolve or absorb into the bloodstream. Undissolved or partially dissolved calcium tablets in the stomach or intestines can absorb X-rays in a manner similar to bone.
Dense, unabsorbed calcium in the digestive tract can lead to an artificial overestimation of bone density, especially in areas like the lumbar spine close to the gastrointestinal system. A falsely elevated BMD reading could mask actual bone loss or lead to an inaccurate diagnosis of osteoporosis or osteopenia. This interference is a concern with supplemental calcium, as dietary calcium from foods is absorbed well before the scan and does not pose the same issue.
Preparing for an Accurate DEXA Scan
To ensure accurate DEXA scan results, patients are advised to avoid calcium supplements for a specific period before the procedure. This timeframe is 24 to 48 hours, though instructions may vary by clinic. If a patient accidentally takes a calcium supplement before their scan, it is important to inform the technician or healthcare provider, who can then assess the situation.
Beyond calcium, other preparatory steps contribute to scan accuracy. Patients should wear loose, comfortable clothing without metal zippers, buttons, or buckles, as metal objects can interfere with the X-ray images. Removing all jewelry and avoiding recent barium studies or injections of contrast material are also recommended to prevent interference with scan measurements.