What are the tests for assessing bone fragility in an individual suspected of having osteoporosis, particularly those with a history of fractures or at high risk due to age, gender, or medical history?

Tests for Assessing Bone Fragility in Osteoporosis

Primary Diagnostic Test

Dual-energy x-ray absorptiometry (DXA) of the lumbar spine and bilateral hips is the gold standard test for assessing bone fragility and diagnosing osteoporosis. 1 DXA accurately predicts fracture risk and has established reproducibility that led to WHO diagnostic standards. 1

DXA Scanning Protocol

• Scan both the lumbar spine (L1-L4) and bilateral hips (total hip and femoral neck) in all patients as the initial assessment. 1, 2
• The distal one-third radius of the nondominant arm should be scanned as a third site when both hips are unavailable or in patients with hyperparathyroidism. 1
• If more than 2 vertebral levels must be excluded due to fracture, facet joint osteoarthritis, or spondylosis causing falsely elevated BMD, use the second hip or distal radius instead of the spine. 1

Interpretation of DXA Results

• T-scores define osteoporosis: T-score ≤ -2.5 indicates osteoporosis, T-score between -1.0 and -2.5 indicates osteopenia, and T-score > -1.0 is normal. 1
• T-scores represent the number of standard deviations the patient's BMD is above or below the mean of a young healthy reference population. 1
• Z-scores (comparison to age-matched controls) should be used to detect secondary causes of osteoporosis rather than for diagnosis. 1
• Use T-scores for all postmenopausal women regardless of age, not Z-scores. 3

Vertebral Fracture Assessment (VFA)

VFA should be performed during the same DXA session for patients with T-score < -1.0 and one or more of the following risk factors: 2

• Women aged ≥70 years or men aged ≥80 years 2
• Historical height loss >4 cm 2
• Self-reported but undocumented prior vertebral fracture 2
• Glucocorticoid therapy equivalent to ≥5 mg prednisone daily for ≥3 months 2

VFA uses low-dose imaging to detect vertebral compression fractures, which are diagnostic of osteoporosis even when BMD values are not in the osteoporotic range. 4, 5

Quantitative Computed Tomography (QCT)

QCT of the lumbar spine and hip provides volumetric BMD and can separately assess trabecular and cortical bone compartments. 1

Key Differences from DXA

• QCT cutoff values differ from WHO criteria: 80-120 mg/mL indicates osteopenia, and <80 mg/mL indicates osteoporosis. 1
• WHO T-score definitions do not apply to QCT spine measurements because they were derived from DXA projectional measurements. 1
• Projectional QCT of the hip provides calculated areal BMD comparable to DXA, allowing use of WHO T-score classifications. 1
• QCT is particularly useful in patients with advanced degenerative spine changes where DXA measurements may be falsely elevated. 1

Quantitative Ultrasound (QUS)

QUS of the calcaneus uses sound wave attenuation to assess bone quality, though it does not measure BMD directly and WHO definitions cannot be applied. 1

• QUS independently predicts fractures in men even though its ability to diagnose DXA-determined osteoporosis is limited. 1
• QUS is nonionizing, portable, and inexpensive, making it useful for outpatient screening settings. 1
• QUS should not replace DXA for definitive diagnosis but may help identify patients who need confirmatory DXA testing. 1

Trabecular Bone Score (TBS)

TBS is software analysis applied to DXA-generated spine images that evaluates skeletal microarchitecture and bone quality rather than bone quantity. 1

Fracture Risk Assessment Tools

FRAX (Fracture Risk Assessment Tool) calculates 10-year probability of hip fracture and major osteoporotic fracture using clinical risk factors with or without BMD. 1, 6

FRAX Components

• Age, sex, height, weight, BMD (optional) 1
• Family history of hip fracture 1
• Current smoking, excess alcohol use 1
• Glucocorticoid use >3 months 1
• Rheumatoid arthritis 1

Treatment is recommended when FRAX shows 10-year hip fracture risk ≥3% or major osteoporotic fracture risk ≥20% in patients with osteopenia (T-score -1.0 to -2.4). 1

Laboratory Tests for Secondary Causes

Basic laboratory evaluation should include: 7

• Serum calcium, phosphate, alkaline phosphatase to screen for hyperparathyroidism and osteomalacia 7
• Complete blood count and serum protein electrophoresis to exclude multiple myeloma 7
• Thyroid function tests 7
• 25-hydroxyvitamin D level 7
• Testosterone level in men 7

Imaging for Suspected Acute Fractures

Plain radiographs (2 views) of the spine are the first examination for suspected vertebral fracture based on acute or subacute symptoms. 1

If initial radiographs are negative but clinical suspicion remains high:

• MRI without contrast is the preferred next test for detecting occult vertebral fractures. 1
• CT without contrast is an alternative if MRI is contraindicated. 1

Common Pitfalls to Avoid

• Do not use peripheral DXA or QUS measurements to diagnose osteoporosis by WHO criteria—only central DXA (spine and hip) measurements apply. 1
• Do not repeat DXA scans more frequently than every 2 years in patients with normal BMD or mild osteopenia, as testing precision limitations prevent reliable measurement of change. 2
• Do not rely solely on spine DXA in patients with degenerative changes, scoliosis, or vertebral fractures, as these falsely elevate BMD—use hip measurements instead. 1, 3
• Do not wait until age 65 (women) or 70 (men) to screen patients with significant risk factors such as glucocorticoid use, fragility fractures, or conditions causing secondary osteoporosis. 1, 2, 3
• A fragility fracture supersedes any DXA measurement—patients with osteopenia who sustain a hip, vertebral, proximal humerus, or pelvic fracture should be diagnosed with osteoporosis. 1, 5