A Dual-energy X-ray Absorptiometry (DEXA) scan is a non-invasive imaging test that measures bone mineral density (BMD) to assess bone strength. Its primary purpose is to monitor bone health and identify conditions like osteoporosis and osteopenia, which involve reduced bone density. Age is a significant factor in determining when these scans are recommended, as bone density naturally changes over a person’s lifespan.
Standard Screening Ages
General guidelines for DEXA scans recommend routine screening for older adults. Women aged 65 and older should undergo a DEXA scan, even without other risk factors for bone loss. For men, routine screening is advised at age 70 and older.
These age recommendations are based on the natural progression of age-related bone loss, which accelerates significantly in postmenopausal women and continues in older men, increasing the risk of osteoporosis and related fractures. For instance, women can lose up to 20% of their bone mass in the first five to seven years after menopause due to declining estrogen levels. While these are standard guidelines, individual circumstances, including medical history and lifestyle, can influence the timing of the first scan.
Factors Prompting Earlier Scans
Individuals younger than the standard screening ages may need a DEXA scan if they have specific risk factors or medical conditions that accelerate bone loss. A history of fragility fractures, which occur from low-energy trauma like a fall from standing height, can prompt earlier screening. Certain medications are known to weaken bones, including long-term use of corticosteroids, some cancer treatments like aromatase inhibitors and androgen deprivation therapy, and certain anti-seizure medications. Proton pump inhibitors, used for acid reflux, can also increase the risk of hip fractures with long-term, high-dose use.
These include autoimmune diseases like rheumatoid arthritis, celiac disease, thyroid disorders, liver or kidney disease, and type 1 diabetes. Lifestyle factors play a role, such as smoking, excessive alcohol intake (more than three servings per day), and a very low body weight (BMI under 19 or bodyweight less than 127 lbs). A family history of osteoporosis or hip fractures in parents can also increase an individual’s risk and warrant earlier evaluation.
Understanding What a DEXA Scan Measures
A DEXA scan primarily assesses bone mineral density (BMD), measuring the amount of calcium and other minerals present in a segment of bone to determine its strength and thickness. The scan works by sending two low-dose X-ray beams with different energy levels through the bones, typically focusing on the lower spine, hip, and sometimes the forearm.
The machine then calculates the bone mineral density by subtracting the absorption of the X-rays by soft tissue from the total absorption. This process allows for the diagnosis of conditions like osteoporosis, a disease causing bones to become very thin and brittle, and osteopenia, a condition where bone density is lower than normal but not yet classified as osteoporosis.
Interpreting Your Bone Density Results
DEXA scan results are presented using two scores: the T-score and the Z-score. The T-score compares an individual’s bone density to that of a healthy young adult (around 30 years old) of the same sex. For postmenopausal women and men aged 50 or older, the T-score is used for diagnostic classification.
A T-score of -1.0 or above indicates normal bone density. A score between -1.0 and -2.5 suggests osteopenia, which is low bone mass. A T-score of -2.5 or lower signifies osteoporosis, indicating significantly weakened bones and an increased fracture risk.
The Z-score compares an individual’s bone density to the average bone density of people of the same age, sex, and body size. This score is particularly useful for premenopausal women, men under 50, and children. A Z-score significantly below average, often considered -2.0 or lower, may suggest that factors other than typical aging, such as underlying medical conditions or medications, are contributing to bone loss, warranting further investigation. It is important to discuss these results with a healthcare provider, as they can offer personalized advice and recommend next steps, which might include lifestyle adjustments, nutritional changes, or medication.