What laboratory tests should be ordered for a patient presenting with back pain?

Laboratory Tests for Back Pain Evaluation

Routine laboratory tests are not recommended for patients with nonspecific back pain without red flags. 1

Initial Assessment and Red Flag Identification

• Laboratory testing should be guided by the presence of red flags identified during history and physical examination 1, 2
• Red flags include: age >50 years, history of cancer, unexplained weight loss, fever, immunosuppression, prolonged steroid use, severe or progressive neurological deficits, duration of pain >4 weeks, and failure to improve with conservative therapy 3, 4
• Psychosocial factors should be assessed as they are stronger predictors of low back pain outcomes than physical examination findings or pain severity 1

Laboratory Tests When Red Flags Are Present

First-line Laboratory Tests

• Complete Blood Count (CBC): To evaluate for infection or inflammation, with leukocytosis suggesting infectious or inflammatory processes 2, 5
• Erythrocyte Sedimentation Rate (ESR): An ESR ≥20 mm/h has 78% sensitivity and 67% specificity for cancer in patients with back pain 2, 3
• C-reactive protein (CRP): Helpful in identifying infection or inflammation 2, 6
• Urinalysis: To evaluate for urinary tract infection or kidney stones, with hematuria indicating urolithiasis and pyuria suggesting urinary tract infection 2

Additional Tests Based on Specific Concerns

• If infection is suspected: Blood cultures, specific serologic tests 5, 7
• If inflammatory conditions are suspected: HLA-B27, rheumatoid factor, anti-nuclear antibodies 4, 6
• If metabolic bone disease is suspected: Calcium, phosphorus, alkaline phosphatase 7

Imaging Considerations

• Imaging should not be routinely obtained in patients with nonspecific low back pain 1
• Plain radiography is recommended for initial evaluation of possible vertebral compression fracture in higher-risk patients (history of osteoporosis or steroid use) 1
• MRI or CT is recommended when severe or progressive neurologic deficits are present or when serious underlying conditions are suspected 1, 2

Clinical Decision Algorithm

1. Assess for red flags during initial evaluation 1, 4
2. If no red flags are present:
   • No laboratory tests needed 1, 5
   • Recommend conservative management 4
3. If red flags are present:
   • Order appropriate laboratory tests (CBC, ESR, CRP, urinalysis) 2, 3
   • Consider targeted imaging based on clinical suspicion 1
4. For persistent symptoms (>4 weeks) despite conservative treatment:
   • Reassess for red flags 1, 4
   • Consider laboratory tests if not previously done 3, 5
   • Consider appropriate imaging studies 1, 7

Common Pitfalls to Avoid

• Ordering unnecessary laboratory tests for acute, nonspecific back pain without red flags 1, 5
• Relying solely on laboratory tests without considering clinical context 6, 7
• Failing to recognize that elevated inflammatory markers (ESR, CRP) have limited specificity and require clinical correlation 3, 7
• Not reassessing patients with persistent symptoms after 4 weeks 1, 4
• Over-reliance on imaging without appropriate laboratory correlation when red flags are present 1, 2