Which lab tests are used to differentiate rheumatoid arthritis (RA) from osteoarthritis (OA)?

Updated: Oct 12, 2020
  • Author: Carlos J Lozada, MD; Chief Editor: Herbert S Diamond, MD  more...
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Rheumatoid arthritis is associated with prominent, prolonged (>1 hour) morning stiffness and overtly swollen, warm joints. Radiographic findings include bone erosion (eg, periarticular osteopenia or marginal erosions of bone) rather than formation. Laboratory findings that further differentiate rheumatoid arthritis from osteoarthritis include the following:

  • Systemic inflammation (elevated erythrocyte sedimentation rate [ESR] or C-reactive protein [CRP] level)

  • Positive serologies (rheumatoid factor [RF] or anti–cyclic citrullinated peptide [anti-CCP] antibodies)

  • Inflammatory joint fluid with a predominance of polymorphonuclear leukocytes (PMNs)

  • Elevated white blood cell (WBC) count

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