What blood tests are indicated for suspected psoriatic arthritis (PsA) or rheumatoid arthritis (RA)?

From the Guidelines

For suspected psoriatic arthritis or rheumatoid arthritis, the recommended initial blood tests include complete blood count (CBC), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), rheumatoid factor (RF), anti-cyclic citrullinated peptide antibodies (anti-CCP), and HLA-B27 genetic testing, as these tests help differentiate between the two conditions and guide treatment decisions 1. When evaluating patients with suspected psoriatic arthritis or rheumatoid arthritis, it is essential to consider the clinical presentation, joint examination, and imaging studies in conjunction with blood test results.

• Key blood tests to order include:
  • CBC to evaluate for anemia of chronic disease
  • ESR and CRP to assess inflammatory markers
  • RF and anti-CCP to differentiate between rheumatoid arthritis and psoriatic arthritis
  • HLA-B27 genetic testing, especially in patients with axial involvement
  • Liver function tests and kidney function tests to monitor for potential medication side effects
• The presence of RF and anti-CCP is more commonly associated with rheumatoid arthritis, while psoriatic arthritis patients may be negative for these markers but positive for HLA-B27 1.
• Inflammatory markers like ESR and CRP are often elevated in both conditions but are not specific, and their levels can be influenced by various factors, including disease activity and treatment response 1.
• Early testing is crucial for prompt diagnosis and treatment initiation to prevent joint damage and disability, and treatment decisions should be guided by a combination of clinical evaluation, laboratory results, and imaging studies 1.

From the Research

Blood Tests for Suspected Psoriatic Arthritis or Rheumatoid Arthritis

• The following blood tests can be used to diagnose and monitor rheumatoid arthritis:
  • Rheumatoid factor (RF) 2, 3
  • Anti-citrullinated protein antibody (anti-CCP) 2, 3
  • C-reactive protein (CRP) 4, 2, 3
  • Erythrocyte sedimentation rate (ESR) 4, 2, 3
  • Complete Blood Count (CBC) 5
  • Serum 14-3-3η level 6
• These tests can help assess disease activity, predict disease severity, and monitor response to treatment 6, 5
• The combination of RF and anti-CCP antibody can be beneficial in confirming a diagnosis of rheumatoid arthritis 2
• Anti-CCP antibody is more specific than other parameters for the diagnosis of rheumatoid arthritis 2, 3
• CBC-derived inflammatory biomarkers such as Neutrophil-to-Lymphocyte Ratio (NLR) can assess disease activity and response to treatment in Rheumatoid Arthritis (RA) 5
• Mean Platelet Volume (MPV) and NLR can determine the prognosis of renal involvement in Systemic lupus erythematosus (SLE) 5
• Red cell distribution width (RDW), MPV, NLR, and platelet to lymphocyte ratio (PLR) are inflammatory biomarkers with a prognostic role in rheumatic disorders that can also assess activity of the disease 5