What laboratory tests are recommended for a patient presenting with symptoms of arthritis?

Arthritis Screen: Recommended Laboratory Tests

For a patient presenting with symptoms of arthritis, order a minimal laboratory panel consisting of: CRP or ESR, complete blood count, liver function tests (transaminases), renal function tests, urinalysis, rheumatoid factor (RF), and anti-citrullinated peptide antibodies (ACPA). 1

Core Inflammatory Markers

• CRP and/or ESR are essential baseline tests that should be performed in all patients with suspected arthritis 1
• CRP is the preferred inflammatory marker as it more accurately reflects acute phase response and correlates better with disease activity than ESR 2, 3
• ESR can be falsely elevated by non-inflammatory factors including immunoglobulins, rheumatoid factor, and anemia, making it less specific than CRP 3
• Critical caveat: Normal inflammatory markers do NOT exclude inflammatory arthritis—40% of rheumatoid arthritis patients have normal ESR or CRP 2, 4

Autoantibody Testing

• Anti-CCP antibodies are the most specific test for rheumatoid arthritis (90% specificity, 60% sensitivity) and should be ordered as part of the initial panel 2, 5
• Rheumatoid factor (RF) provides complementary diagnostic information with 70% specificity and should be included in the initial workup 1, 2
• Both RF and ACPA are predictive of RA diagnosis and prognosis, but negative tests do not exclude progression to RA—seronegative RA accounts for 20-30% of cases 1, 2, 4

Baseline Safety and Organ Function Tests

• Complete blood count with differential to assess for cytopenias and guide treatment decisions 1, 2
• Liver function tests (transaminases) are mandatory before initiating disease-modifying therapy 1
• Renal function tests to establish baseline and guide medication dosing 1, 2
• Urinalysis to screen for renal involvement or other systemic manifestations 1

Conditional Testing Based on Clinical Features

• Antinuclear antibodies (ANA) should be ordered if the diagnosis remains uncertain after initial workup or if connective tissue disease is suspected 1, 2
• HLA-B27 testing is indicated when symptoms suggest spondyloarthropathy, reactive arthritis, or axial involvement 1, 2
• Additional autoantibodies (anti-Ro, anti-La, anti-Sm, anti-RNP, anti-dsDNA) should be considered if systemic inflammatory disorder or connective tissue disease is suspected 1, 2

Grade 2-3 Inflammatory Arthritis Workup

For patients with moderate to severe symptoms (CTCAE grade 2-3), expand the laboratory panel to include: 1

• ANA, RF, anti-CCP antibodies
• ESR and CRP
• Consider imaging (plain X-rays of affected joints, joint MRI, or musculoskeletal ultrasound) 1

Common Pitfalls to Avoid

• Do not delay treatment waiting for positive serology—early aggressive therapy prevents irreversible joint damage, and seronegative RA has similar prognosis to seropositive disease 2
• Do not dismiss inflammatory arthritis based on normal inflammatory markers—acute phase reactants are poor predictors and can be normal even in active disease 2, 4
• Refer to rheumatology within 6 weeks if inflammatory arthritis is suspected, regardless of autoantibody results, as early specialist evaluation improves outcomes 2
• Erosive joint damage can occur within weeks of symptom onset, making early rheumatology involvement critical 1

Monitoring After Initial Workup

• Repeat CRP and ESR every 4-6 weeks after treatment initiation to monitor disease activity and treatment response 2
• Serial inflammatory markers guide treatment escalation but should not be the sole determinant of treatment decisions 2