Which laboratory tests are most useful in confirming a diagnosis of reactive arthritis in a primary care setting?

Laboratory tests most useful in confirming a diagnosis of reactive arthritis in primary care include:

• Inflammatory markers: C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) may be elevated but normal results do not exclude the diagnosis of spondyloarthritis including reactive arthritis.
• HLA-B27 testing: This genetic marker is often associated with reactive arthritis and other spondyloarthritides; a positive test supports the diagnosis but a negative test does not exclude it.
• Microbiological tests: Testing for recent or current genitourinary or gastrointestinal infections (e.g., Chlamydia trachomatis, enteric bacteria) may support the diagnosis since reactive arthritis often follows such infections.

Definitive diagnosis requires specialist assessment and imaging, and laboratory tests in primary care mainly support clinical suspicion rather than confirm diagnosis.

Referral to rheumatology is recommended for suspected cases for further evaluation and confirmation.

Note: There are no specific blood tests that confirm reactive arthritis; diagnosis is clinical supported by laboratory and imaging findings.

References: NICE NG65, NICE CKS