A Dual-Energy X-ray Absorptiometry (DEXA) scan is a specialized medical imaging procedure that uses very low-dose X-rays to assess bone health. The primary purpose of this quick and non-invasive test is to measure Bone Mineral Density (BMD), typically in the hip and spine. The DEXA scan quantifies the mineral content in bone, providing a numerical snapshot of bone strength. This measurement is fundamental for diagnosing conditions like osteoporosis, which causes bones to become weak and brittle. Identifying low bone density allows health professionals to intervene early and reduce the risk of future fractures.
Standard Age Guidelines for Routine Screening
For individuals without specific risk factors, major health organizations recommend starting routine DEXA screening at specific age-based thresholds. This preventative screening targets populations where the natural decline in bone density significantly increases fracture risk. For women, the standard recommendation is to begin screening at age 65, corresponding to the period when postmenopausal bone loss has accelerated.
Men generally experience bone loss at a slower rate than women and typically begin routine screening later. The standard age for men without risk factors is 70 years old. These guidelines are designed to capture individuals developing low bone density (osteopenia) or the more severe condition of osteoporosis. Screening at these ages allows for timely diagnosis and the initiation of treatment before a debilitating fracture occurs.
Medical Conditions and Risk Factors Requiring Earlier Testing
While ages 65 and 70 are benchmarks for routine screening, certain medical histories and lifestyle factors warrant a DEXA scan starting earlier. Postmenopausal women under age 65, and men aged 50 to 69, should be considered for early testing if they possess specific risk indicators. A history of a fragility fracture after age 50 is a strong indication, suggesting the underlying bone structure may already be compromised.
Long-term use of certain medications is a major cause of secondary osteoporosis that necessitates earlier screening. This includes taking glucocorticoids, such as prednisone, at a dose of 5 milligrams or more daily for three months or longer. These steroid medications interfere with bone formation and accelerate bone breakdown, rapidly lowering BMD.
Numerous chronic medical conditions also affect bone metabolism and may require screening in a patient’s 50s or earlier. Conditions like rheumatoid arthritis, hyperparathyroidism, and malabsorption disorders such as Celiac disease contribute to accelerated bone loss. Low body weight, defined as a Body Mass Index (BMI) below 18.5 or less than 127 pounds, is an independent risk factor for low bone density. Early menopause (before age 40) removes the protective effects of estrogen sooner, making earlier DEXA evaluation appropriate.
Interpreting Your Bone Density Results
The results of a DEXA scan are reported using two standardized values: the T-score and the Z-score. The T-score is used to formally diagnose osteopenia and osteoporosis in postmenopausal women and men aged 50 and older. This score compares the patient’s Bone Mineral Density to that of a healthy young adult of the same sex, expressed in standard deviation units.
A T-score of -1.0 or higher is considered normal bone density. A score between -1.0 and -2.5 indicates osteopenia. A T-score of -2.5 or lower signifies osteoporosis, confirming an increased risk of fracture.
The Z-score compares the patient’s BMD to the average density of individuals who are the same age, sex, and ethnicity. This score is relevant for younger adults, premenopausal women, and men under age 50. A Z-score below -2.0 is considered “below the expected range for age” and suggests that factors other than normal aging, such as an underlying medical condition, may be causing the bone loss.