Which laboratory tests are recommended for confirming a diagnosis of JIA and ruling out other conditions?

Recommended laboratory tests for confirming juvenile idiopathic arthritis (JIA) and excluding other conditions include:

• Full blood count (FBC) to assess for anaemia or infection, which can help exclude infectious or haematological causes of joint symptoms NICE CKS.
• Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) as markers of systemic inflammation; elevated levels support an inflammatory arthritis diagnosis but are not specific to JIA NICE CKS.
• Rheumatoid factor (RF) testing, which is positive in a minority of JIA cases and helps classify subtypes; a negative RF does not exclude JIA NICE CKS.
• Antinuclear antibody (ANA) testing, useful for identifying patients at risk of uveitis and supporting diagnosis, though not diagnostic alone NICE CKS.
• Exclusion of other conditions through relevant tests such as blood cultures or serology if infection is suspected, and metabolic or malignancy screens as clinically indicated NICE CKS.
• Recent pediatric rheumatology literature emphasizes the importance of a comprehensive rheumatology panel including these tests to differentiate JIA from mimicking conditions and to guide early specialist referral Pilania & Singh 2019.

In summary, no single laboratory test confirms JIA; diagnosis is clinical supported by inflammatory markers (ESR, CRP), autoantibodies (RF, ANA), and exclusion of other causes via FBC and targeted investigations NICE CKS Pilania & Singh 2019.