There are no laboratory tests that are specific for PsA. Acute phase reactants such as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) may become elevated, as they do in most inflammatory diseases, and are markers of severe disease. Patients with PsA typically have lower levels of ESR and CRP than patients with rheumatoid arthritis. However, a normal ESR and CRP should not be used to rule out a diagnosis of PsA.
Patients with PsA are typically seronegative for rheumatoid factor, although it is detected in 5%-9% of cases. Negative rheumatoid factor is often seen in PsA.
Serum immunoglobulin A levels are increased in two thirds of patients with PsA and in one third of patients with psoriasis.
Learn more about the workup for PsA.
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Cite this: Herbert S Diamond, Anwar Al Hammadi, Eric M. Ruderman, et. al. Fast Five Quiz: Can You Identify Psoriatic Arthritis and Initiate the Best Treatment Practices? - Medscape - Jan 25, 2023.