Juvenile Idiopathic Arthritis

3.1 What laboratory tests are needed? At the time of diagnosis, certain laboratory tests are useful along with joint examination and eye checks. These tests help to define the type of JIA and to identify patients at risk of developing specific complications such as chronic iridocyclitis. Rheumatoid factor (RF) is a laboratory test detecting an autoantibody, which, if positive and persistent in high concentration, indicates the JIA subtype. Antinuclear antibodies (ANA) are often positive tests in patients with oligoarticular early-onset JIA. This population of JIA patients are at high risk of developing chronic iridocyclitis and therefore should have scheduled eye screenings using a slit-lamp (every three months). HLA-B27 is a cellular marker which is positive in up to 80% of patients with enthesitis-associated arthritis. It is positive in only 5-8% of healthy individuals. Other examinations such as erythrocyte sedimentation rate (ESR) or Creactive protein (CRP) that measure the extent of general inflammation are useful; however, diagnosis as well as treatment decisions are based much more on clinical assessment than on laboratory tests. Depending on the treatment, patients may need periodic tests (such as blood cell count, liver function test, urine test) to check for side effects of the treatment and to assess potential drug toxicity that may cause no symptoms. The inflammation in the joint is evaluated mainly by clinical examination and sometimes imaging studies such as ultrasound. Periodic X-rays or magnetic resonance imaging (MRI) may be useful to assess bone health and bone growth and therefore to tailor the therapy.