What laboratory tests should be ordered for a patient with osteoporosis?

Laboratory Tests for Patients with Osteoporosis

For patients with osteoporosis, a comprehensive laboratory workup should include basic metabolic tests, tests to identify secondary causes, and additional tests based on clinical suspicion to guide appropriate management and treatment decisions. 1, 2

Basic Laboratory Tests

• Serum calcium and phosphate to assess bone metabolism and identify abnormalities 1, 2
• 25-hydroxyvitamin D level to identify vitamin D deficiency, which is common in osteoporosis 2
• Albumin or total protein to correctly interpret calcium levels 1, 2
• Serum creatinine to assess kidney function 1, 2
• Complete blood count to rule out hematologic disorders 1, 2
• Serum alkaline phosphatase to evaluate bone turnover 1

Tests to Identify Secondary Causes of Osteoporosis

Secondary causes of osteoporosis are present in 44-90% of patients with low bone mineral density and should be ruled out with appropriate testing 1, 3:

• Thyroid function tests (TSH) to rule out hyperthyroidism 2, 4
• Intact parathyroid hormone (iPTH) if calcium levels are abnormal 1, 2
• Sex hormone levels 2, 5:
  • In men: serum testosterone, especially in men under 70 years 5
  • In women: consider estradiol, LH, FSH if clinically indicated 2
• Liver function tests if liver disease is suspected 1, 2

Additional Tests Based on Clinical Suspicion

• Erythrocyte sedimentation rate (ESR) if inflammatory conditions are suspected 1, 2, 6
• 24-hour urine calcium in men to evaluate for hypercalciuria 5
• Protein electrophoresis to rule out multiple myeloma, especially in patients with unexplained osteoporosis 1, 5, 4
• Urinary markers of bone collagen degradation (such as N-telopeptides) if monitoring treatment response 7

Testing Algorithm

1. First-line laboratory tests (for all patients with osteoporosis) 1, 2, 4:

   • Serum calcium (corrected for albumin)
   • Phosphate
   • Creatinine
   • Albumin
   • Complete blood count
   • Alkaline phosphatase
   • 25-hydroxyvitamin D
   • TSH
   • ESR

2. Second-line tests (based on clinical suspicion) 1, 2, 5:

   • Parathyroid hormone (if calcium abnormal)
   • Testosterone in men under 70 years
   • Protein electrophoresis
   • 24-hour urine calcium (especially in men)
   • Liver function tests

Important Considerations

• This comprehensive testing panel has 92% sensitivity for detecting secondary causes of osteoporosis 1, 3
• Common secondary causes include hypogonadism (40-60% of cases in men) and estrogen deficiency (35-40% in premenopausal women) 1, 3
• Patients with secondary osteoporosis have a 2-3 fold higher risk of hip and vertebral fractures 1, 3
• Laboratory testing should be performed before initiating treatment to identify potentially reversible causes of bone loss 1, 4
• Testing for bone turnover markers may be useful for monitoring treatment response but is not routinely recommended for initial diagnosis 1, 7

Pitfalls to Avoid

• Relying solely on bone mineral density without laboratory testing may miss treatable secondary causes 1, 5
• Normal calcium levels do not rule out bone disease, as they may be maintained through bone calcium mobilization 1
• Vitamin D deficiency is common and may not be clinically apparent without testing 2, 8
• Multiple secondary causes can coexist in the same patient, even when one cause is already known 5
• Excessive or insufficient testing - follow a systematic approach based on clinical presentation 1, 2