RF (Rheumatoid Factor)

What it is: A test designed to detect and measure levels of a specific antibody directed against the blood component immunoglobulin G (IgG).

Why doctors order it: A positive RF is found in adults with rheumatoid arthritis. If the test is positive, it helps your child’s doctor determine both the form of JRA he or she has and how aggressively to treat it. “Children – primarily girls – with RF-positive JRA truly have rheumatoid arthritis and, therefore, are at greatest risk for joint erosions, rheumatoid nodules and poor functional outcome,” says Dr. Szer.

Test limitations: Fortunately, unlike adults, 90 percent of children who have JRA do not have a positive RF.


ANA (Antinuclear Antibody)

What it is: A test that measures the presence of an antibody directed against structures in the child’s cells’ nuclei.

Why doctors order it: A positive ANA is associated with many kinds of arthritis and with other rheumatic conditions such as lupus, scleroderma and mixed connective tissue disease. In young girls with pauciarticular JRA, a positive ANA may be associated with a higher risk of uveitis.

Test limitations: Many rheumatic conditions have a positive ANA, and up to 20 percent of all children have positive ANAs, so the presence of ANA alone doesn't necessarily indicate a problem.


Beyond Lab Tests

These are just a few of the more common tests your child’s doctor may order. There are also many other types of tests – including X-rays, bone scans and biopsies – that doctors may use to help them better understand your child’s disease. Yet every test has its limitations, and no test in itself can diagnose arthritis. The right tests, along with your doctor’s own observations and your participation in the process, can help your child get the right diagnosis and the safest and most effective treatment.