What is the diagnostic approach for osteoporosis?

Diagnostic Approach for Osteoporosis

Dual-energy X-ray absorptiometry (DXA) of the hip and lumbar spine is the gold standard for diagnosing osteoporosis, with diagnosis based on WHO criteria: T-score ≤ -2.5 indicates osteoporosis, T-score between -1.0 and -2.4 indicates osteopenia, and T-score > -1.0 is normal. 1

Screening Recommendations by Population

Women

• All women age 65 years and older require screening 1
• Women younger than 65 years should be screened if they have risk factors including: 1
  • Estrogen deficiency
  • Maternal hip fracture after age 50
  • Low body weight
  • History of amenorrhea
  • Current smoking
  • Loss of height or thoracic kyphosis

Men

• All men age 70 years and older require screening 1
• Men younger than 70 years should be screened if they have risk factors including: 1
  • Low BMI or weight loss
  • Physical inactivity
  • Oral corticosteroid use
  • Androgen deprivation therapy
  • Previous fragility fracture

Step-by-Step Diagnostic Algorithm

Step 1: Bone Mineral Density Testing

• Measure BMD at the proximal femur and lumbar spine using DXA 1
• DXA has 90-95% sensitivity for detecting osteoporosis 1
• Interpret using T-scores for postmenopausal women and men ≥50 years 1
• Use Z-scores for premenopausal women, adults <50 years, and children 2

Step 2: Fracture Risk Assessment

• For patients with T-scores between -1.0 and -2.4 (osteopenia), calculate 10-year fracture probability using the FRAX tool 1
• FRAX incorporates BMD and clinical risk factors to predict major fracture and hip fracture risk 2

Step 3: Vertebral Fracture Assessment

• Review previous imaging studies (spine radiographs, CT scans, or MRI) to identify missed vertebral fractures 3
• Plain radiographs of thoracic and lumbar spine or DXA with vertebral fracture assessment software may be useful in patients with osteopenia and height loss, with 80-90% sensitivity 3

Step 4: Laboratory Evaluation to Exclude Secondary Causes

All patients with suspected or confirmed osteoporosis require laboratory testing, as secondary causes are present in 32-85% of previously undiagnosed cases 3

Essential Laboratory Tests (92% sensitivity for detecting secondary causes):

• Complete blood count (CBC) 3
• Serum calcium 3
• Serum phosphorus 3
• Serum creatinine 3
• Alkaline phosphatase 3
• 25-hydroxyvitamin D [25(OH)D] 3
• Thyroid-stimulating hormone (TSH) 3
• Parathyroid hormone (PTH) 3

Sex-Specific Testing:

• Men with osteoporosis: assess for hypogonadism 3
• Premenopausal women with osteoporosis: evaluate for clinical estrogen deficiency or primary ovarian failure 3

Additional Testing Based on Clinical Suspicion:

• Suspected multiple myeloma: serum protein electrophoresis (80-90% sensitivity) 3
• Suspected malabsorption: tissue transglutaminase antibodies for celiac disease (90-95% sensitivity) 3
• Suspected Cushing's syndrome: cortisol testing (95-100% sensitivity) 3

Alternative Screening Tests (Not Recommended for Diagnosis)

• Calcaneal ultrasonography has only 75% sensitivity and 66% specificity and is not sufficiently accurate to replace DXA 1
• Osteoporosis Self-Assessment Tool (OST) has only 81% sensitivity and 68% specificity and should not substitute for DXA 1
• Quantitative CT (QCT) provides volumetric BMD but is more expensive and less widely available than DXA 1

Follow-Up Testing Intervals

• If initial DXA does not warrant treatment, repeat testing every 2-5 years depending on proximity to treatment thresholds 1, 3
• Patients on bone loss-inducing medications or with baseline BMD near treatment threshold require DXA every 2 years or more frequently 1, 3

Critical Pitfalls to Avoid

Do Not Miss Secondary Causes

The most common secondary causes vary by population: 3

• Men: hypogonadism, alcoholism, glucocorticoid exposure
• Premenopausal women: estrogen deficiency, glucocorticoid exposure

Do Not Overlook Vitamin D Deficiency

• Vitamin D deficiency is present in 32-85% of osteoporotic patients and causes osteomalacia with bone pain, muscle weakness, and stiffness 3
• This requires special attention as it is both highly prevalent and treatable 3

Do Not Use T-Scores in Wrong Populations

• T-scores are only appropriate for postmenopausal women and men ≥50 years 1
• BMD alone is not diagnostic of osteoporosis in men <50 years 2

Do Not Rely on Alternative Tests Alone

• Alternative screening tools lack sufficient sensitivity and specificity to replace DXA for diagnosis 1