What lab tests should I order for a client with a high antinuclear antibody (ANA) titer, psoriasis, and chronic pain in multiple major joints?

Laboratory Tests for a Client with High ANA, Psoriasis, and Chronic Joint Pain

For a client with ANA >160, psoriasis, and chronic pain in multiple major joints, you should order a comprehensive panel of laboratory tests to evaluate for psoriatic arthritis (PsA) and rule out other rheumatologic conditions. 1

Initial Laboratory Evaluation

• Acute phase reactants:

  • C-reactive protein (CRP) - to assess inflammation level 2, 1
  • Erythrocyte sedimentation rate (ESR) - elevated ESR is associated with poor prognosis and progressive joint damage 2

• Autoimmune panel:

  • Rheumatoid factor (RF) - typically negative in PsA (seronegative arthritis) 1, 3
  • Anti-cyclic citrullinated peptide (anti-CCP) antibodies - to differentiate from rheumatoid arthritis 2, 4
  • Further ANA profile with specific nuclear antigens - to evaluate for other autoimmune conditions 5

• HLA testing:

  • HLA-B27 - especially if symptoms affect the spine or suggest reactive arthritis 2, 4

Additional Laboratory Tests

• Complete blood count (CBC) - to assess for anemia of chronic disease and evaluate eosinophil counts (which can be elevated in some patients with psoriasis on biologics) 6

• Metabolic panel - to evaluate liver and kidney function before starting treatment 2, 1

• Uric acid levels - to rule out gout as a cause of joint pain 3

Imaging Studies

• Plain radiographs of affected joints - to evaluate for erosions and joint damage 2, 1

• Ultrasound or MRI of affected joints - if clinically indicated to assess for synovitis, enthesitis, and early inflammatory changes not visible on plain films 2, 4

Special Considerations

• Arthrocentesis (joint fluid analysis) may be necessary if there is joint swelling to rule out crystal arthropathy or infection 2, 3

• Specific autoantibody testing: Consider testing for antibodies against dense fine speckled 70 (DFS70), which has been found in approximately 6.5% of patients with psoriatic disease 5

• Monitor autoantibody levels: ANA titers may increase with certain biologic treatments, particularly TNF inhibitors like infliximab (14% increase) 6, 7

Interpretation of Results

• The presence of positive ANA is not uncommon in PsA patients (16.6-25% depending on subtype) but doesn't necessarily indicate another autoimmune disease 8

• Negative RF and anti-CCP with positive ANA supports PsA diagnosis rather than rheumatoid arthritis 1, 3

• Elevated inflammatory markers (CRP, ESR) indicate active disease and are associated with poor prognosis 2

• Laboratory tests in PsA are often nondiagnostic, and diagnosis relies heavily on clinical presentation and the CASPAR criteria 2, 3

Follow-up Testing

• After initiating treatment, monitor inflammatory markers (CRP, ESR) every 4-6 weeks to assess treatment response 2

• Consider periodic reassessment of autoantibodies, as some biologics may decrease nuclear antigen autoreactivity over time 5