Work-up for Osteoporosis
Dual-energy X-ray absorptiometry (DXA) of the lumbar spine and hip is the primary diagnostic test for osteoporosis, supplemented by targeted laboratory testing to identify secondary causes of bone loss. 1, 2
Primary Imaging Assessment
DXA scanning of the lumbar spine (L1-L4) and both hips (femoral neck and total hip) is the gold standard for diagnosing osteoporosis and predicting fracture risk. 1, 2 This imaging modality has been clinically validated to accurately predict fracture risk and correlates directly with the amount of force necessary to fracture bone. 1
Indications for DXA Testing
Obtain DXA screening in the following populations:
- All women ≥65 years and all men ≥70 years (asymptomatic screening) 1
- Women <65 years or men <70 years with risk factors including:
- Any individual ≥50 years with a fragility fracture (wrist, hip, spine, or proximal humerus with minimal trauma) 1
- Any individual with insufficiency fractures at any age 1
Alternative Imaging When DXA is Limited
For patients with advanced degenerative spine changes, scoliosis, or conditions that spuriously elevate BMD measurements, consider:
- DXA of the distal one-third radius (nondominant forearm) 1, 2
- Quantitative CT (QCT) of the lumbar spine and hip 1, 2
These alternatives avoid the falsely elevated readings caused by facet joint osteoarthritis, vertebral fractures, or spondylosis. 1
Vertebral Fracture Assessment
Add vertebral fracture assessment (VFA) via DXA for patients with T-scores <-1.0 and any of the following:
- Women ≥70 years or men ≥80 years 1
- Historical height loss >4 cm (>1.5 inches) 1
- Self-reported but undocumented prior vertebral fracture 1
- Glucocorticoid therapy ≥5 mg prednisone equivalent daily for ≥3 months 1
VFA is performed concomitantly with DXA at the same visit, providing point-of-care assessment for vertebral compression fractures. 1
Laboratory Evaluation for Secondary Causes
A focused laboratory panel is essential to detect secondary causes of osteoporosis, which can be identified in the majority of cases with appropriate testing. 1 The following tests have 92% sensitivity for detecting secondary causes when no obvious etiology is apparent from history and physical examination: 1
Essential Laboratory Tests
- Complete blood count (CBC) to assess for hematologic disorders 1, 2
- Comprehensive metabolic panel including:
- 25-hydroxyvitamin D [25(OH)D] level 1, 3
- Parathyroid hormone (PTH) if hyperparathyroidism is suspected 1, 2
- Serum phosphorus to detect phosphate wasting or osteomalacia 1
- Lactate dehydrogenase (LDH) and alkaline phosphatase as markers of bone turnover 1, 3
Additional Testing When Indicated
Consider these tests based on clinical suspicion:
- Thyroid-stimulating hormone (TSH) if hyperthyroidism suspected 4
- Serum protein electrophoresis if multiple myeloma is a concern 1
- Testosterone level in men with suspected hypogonadism 4, 5
- 24-hour urine calcium if hypercalciuria suspected 1
Diagnostic Interpretation
Osteoporosis is diagnosed when DXA shows a T-score ≤-2.5 at the lumbar spine, femoral neck, or total hip. 2, 3, 6 The T-score compares the patient's BMD to young-adult reference populations. 2
A fragility fracture (particularly vertebral or hip) establishes the diagnosis of osteoporosis regardless of T-score. 2, 3 Most fragility fractures actually occur in individuals with T-scores higher than -2.5, confirming that the fracture itself demonstrates skeletal fragility. 2
Risk Stratification Beyond BMD
For patients with osteopenia (T-score between -1.0 and -2.5), calculate 10-year fracture risk using the WHO Fracture Risk Assessment Tool (FRAX). 1 Treatment should be considered if:
Note that FRAX has not been validated in certain populations (e.g., HIV-infected patients) and may underestimate fracture risk in these groups. 1
Special Populations
Premenopausal Women and Men <50 Years
Use Z-scores (comparison to age-matched controls) rather than T-scores to detect secondary causes of osteoporosis in these populations. 2 DXA is still appropriate for initial imaging when risk factors are present. 1
Patients on Chronic Glucocorticoids
Obtain DXA with VFA or dedicated spine X-rays as soon as possible for adults initiating or continuing glucocorticoids ≥2.5 mg/day for >3 months. 7 These patients have dramatically elevated vertebral fracture risk (>50% prevalence in those over 70 years). 8
For acute back pain in glucocorticoid users, obtain standard 2-view X-rays of the symptomatic spine region first, not MRI. 7
Spine Surgery Candidates
Preoperative testing with DXA (T-score <-2.5), CT (Hounsfield units <97.9), or serum vitamin D3 (<20 ng/mL) predicts increased risk of postoperative adverse events in patients undergoing spinal instrumentation. 1 One of these tests should be performed preoperatively in patients with suspected osteoporosis. 1
Common Pitfalls to Avoid
Do not rely on plain radiographs for osteoporosis diagnosis—radiographic evidence of bone loss is not apparent until 30-40% of bone mass has been lost. 2 Plain films are appropriate only for evaluating suspected acute fractures. 2
Do not skip evaluation for secondary causes, particularly in premenopausal women, men under 50, and patients with very low Z-scores. 1, 2 Secondary osteoporosis accounts for a substantial proportion of cases and requires specific treatment. 1
Do not ignore degenerative changes that can falsely elevate lumbar spine BMD measurements—use alternative sites (forearm or QCT) when significant spondylosis, facet arthropathy, or scoliosis is present. 1, 2
Do not overlook asymptomatic vertebral fractures—more than 65% of vertebral fractures are clinically silent, and their presence changes risk stratification to very high risk requiring immediate treatment. 2, 7
Do not forget vitamin D assessment—vitamin D deficiency is highly prevalent and treatable, with levels <20 ng/mL associated with increased fracture risk. 1 Adequate repletion (800-1000 IU daily for maintenance) is essential for bone health. 1, 3