Which laboratory tests are essential for the initial assessment of a patient with suspected inflammatory arthritis?

For the initial assessment of a patient with suspected inflammatory arthritis, the essential laboratory tests include:

• Rheumatoid factor (RF) testing, offered to adults with suspected rheumatoid arthritis who have synovitis on clinical examination.
• Anti-cyclic citrullinated peptide (anti-CCP) antibodies, considered especially if rheumatoid factor is negative, to aid diagnosis of rheumatoid arthritis.
• Inflammatory markers such as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) may be measured, although normal results do not exclude inflammatory arthritis.
• Serum urate level measurement if gout is suspected, to confirm diagnosis (a level of 360 micromol/litre or more supports gout).
• HLA-B27 testing may be considered in suspected spondyloarthritis cases, particularly if psoriasis or relevant symptoms are present.

These tests should not delay urgent referral for specialist opinion if persistent synovitis is present.

Additionally, joint aspiration and synovial fluid analysis may be considered if diagnosis remains uncertain, particularly to exclude septic arthritis or crystal arthropathies.

Imaging such as X-rays of hands and feet is also recommended but is outside the scope of laboratory tests.

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