What laboratory investigations are required for monitoring rheumatoid arthritis?

Laboratory Monitoring for Rheumatoid Arthritis

For monitoring rheumatoid arthritis, you need two categories of laboratory tests: disease activity monitoring (inflammatory markers incorporated into composite measures every 1-3 months during active disease) and medication safety monitoring (CBC, liver transaminases, and creatinine with frequency determined by your specific DMARD regimen). 1, 2

Disease Activity Monitoring Labs

Inflammatory Markers

• C-reactive protein (CRP) is preferred over ESR because it is more reliable, not age-dependent, and provides better reproducibility 2, 3
• ESR and CRP are incorporated into validated composite disease activity measures (DAS28-ESR, DAS28-CRP, and SDAI) that guide treatment decisions 1, 3
• Measure disease activity every 1-3 months until remission is achieved, then every 3-6 months once remission or low disease activity is maintained 1

Critical caveat: Approximately 40-50% of patients with active RA can have normal acute phase reactants—do not dismiss disease activity based solely on normal ESR/CRP 3

Composite Disease Activity Measures

The American College of Rheumatology recommends using one of six validated measures, with your choice depending on available resources 1:

• RAPID-3 or PAS/PAS-II: Patient-reported measures requiring no lab work, ideal for limited resources 1
• CDAI: Requires joint counts but no lab results, includes 28 tender/swollen joint counts plus patient and provider global assessments 1
• SDAI: Includes CDAI components plus CRP, requiring lab access 1
• DAS28-ESR or DAS28-CRP: Complex formula incorporating joint counts, patient global assessment, and inflammatory markers 1

Medication Safety Monitoring

For Methotrexate, Leflunomide, or Sulfasalazine

Monitor CBC, liver transaminases, and serum creatinine with this specific schedule 2:

• Every 2-4 weeks during the first 3 months of therapy or after dose increases
• Every 8-12 weeks between months 3-6 on stable therapy
• Every 12 weeks after 6 months on stable therapy

Do not use less frequent monitoring prematurely—maintain the every 2-4 week schedule for the full first 3 months 1

For Hydroxychloroquine

• No routine laboratory monitoring required after baseline labs 2, 3

For NSAIDs

• Monitor CBC, liver function tests, and renal function tests every 6-12 months 2, 3

For Tocilizumab (Actemra)

• Monitor CBC and liver function tests within the first 1-2 months, then every 3-4 months thereafter 2
• Monitor lipid profiles every 6 months 2

For Tofacitinib

• Monitor lipid profiles at baseline and periodically 2

Baseline Laboratory Assessment

Before starting any DMARD therapy, obtain 3:

• Complete blood count with differential (assess for cytopenias, calculate neutrophil-to-lymphocyte ratio)
• Comprehensive metabolic panel (liver function, renal function, glucose, uric acid)
• Urinalysis
• ESR and CRP (establish baseline inflammatory status)

Pre-Biologic Screening

Before initiating biologic therapy, mandatory screening includes 2, 3:

• Tuberculosis screening: Tuberculin skin test or interferon-gamma release assay (IGRA preferred if prior BCG vaccination)
• Hepatitis B: Surface antigen, surface antibody, and core antibody
• Hepatitis C antibody

Annual TB testing is required for patients on biologics who live, travel, or work where TB exposure is likely 2

Practical Implementation Algorithm

1. At diagnosis: Obtain baseline labs (CBC, CMP, urinalysis, ESR, CRP) and select a composite disease activity measure based on your practice resources 1, 3

2. Before starting DMARDs: Complete pre-treatment screening (TB, hepatitis B/C if biologics planned) 2, 3

3. During active disease: Measure disease activity with your chosen composite measure every 1-3 months, incorporating CRP or ESR as appropriate 1

4. DMARD-specific monitoring: Follow the medication-specific laboratory schedule based on your patient's regimen 2

5. Once remission/low disease activity achieved: Reduce disease activity monitoring to every 3-6 months while maintaining medication-specific safety monitoring 1

6. Patients with comorbidities or abnormal results: May require more frequent testing than standard intervals 2

Key pitfall to avoid: Do not switch between different composite disease activity measures arbitrarily, as this affects longitudinal tracking and makes it difficult to assess true disease progression 1