Antinuclear Antibody Test in Children
What is an antinuclear antibody?
An antibody is a protein made by white blood cells (B cells). Antibodies help defend against invaders (for example, viruses and bacteria) that cause disease or infection in the body. When antibodies make a mistake by recognizing our “self” cells as being “foreign,” they are called autoantibodies.
Most of us have autoantibodies, but usually a very small amount. If there are enough autoantibodies present, a cascade of inflammation (swelling) is started. This causes our immune system to attack our own body (autoimmune disease).
An antinuclear antibody (ANA) is an autoantibody that mistakenly binds to normal protein within the nucleus of a cell. ANAs are usually found in people who have autoimmune conditions such as systemic lupus erythematosus. They may also be seen in other autoimmune diseases, such as mixed connective tissue disease, Sjogren's syndrome, dermatomyositis, polymyositis and scleroderma.
However, not everybody who has ANAs has an autoimmune disease. For instance, ANAs could be found in 10-15 percent of completely healthy children. They could be briefly present in the setting of intercurrent infection (an infection that occurs while the person already has another infection) or in people who are taking certain drugs (for example, hydralazine, isoniazid, procainamide, and some anticonvulsants).
How is a test for antinuclear antibody performed?
Because ANAs can be present in various situations, the ANA test is not used to make a diagnosis, but simply to suggest to the doctor the possibility of autoimmune disease.
To perform an ANA test, a blood sample is taken from a vein and sent to a laboratory for testing.
One form of ANA test is called the ELISA. In this test, the person's blood sample is mixed with antigens (portions of proteins that bind antibodies). If the antibody for that antigen is in the blood, the test can find it.
Laboratories often use ELISA as a first screening, but will follow up with another test called the Fluorescent Antinuclear Antibody (FANA) test to confirm the results. FANA results are reported in titers and the pattern of autoantibodies made (homogeneous, speckled, centromere, etc.).
Titer reading is determined by adding saline (salt water) to a sample of plasma (the protein-rich liquid part of blood) a certain number of times. For example, one part of plasma mixed with 40 parts of saline is a 1:40 mixture. This mixture is called a "titer." The mixture is then taken through a series of additional steps of dilution (watering down), creating tubes of 1:80, 1:160, 1:320, and 1:640 mixture, respectively. If an ANA is found at higher titer, it indicates a higher amount of ANAs.
How is an antinuclear antibody test used?
An ANA test is usually not performed as part of a routine physician visit. Instead, the test should be ordered only when there is a strong chance that a child's symptoms are caused by an ANA-positive rheumatic disease such as lupus, Sjogren’s syndrome, or mixed connective tissue disease.
An ANA test should not be ordered as a screening test for non-specific complaints such as musculoskeletal pain, fever or rash.
The ANA test is also used as a prognostic marker (a way of telling ahead of time) in children with juvenile idiopathic arthritis (JIA). (The ANA test is not used to diagnose JIA.) Those children who have a positive ANA test are at higher risk of having uveitis (inflammation inside the eye); therefore, they require more frequent eye exams by an ophthalmologist (eye doctor) compared to JIA patients with negative ANA status.
Results and Follow-Up
What should I do if my child has a positive ANA test?
Your physician or pediatric rheumatologist will interpret the ANA test in the context of other laboratory studies and your child’s history and physical examination to determine if your child has any sign of ANA-related rheumatologic disease. Further testing will be done if the doctor suspects your child has a particular disease.
ANA testing has a high "false positive" rate, meaning that many people who don't have an autoimmune disease can have higher ANA levels. It is important to speak with your child’s pediatrician or pediatric rheumatologist to determine if a positive ANA result is meaningful or if it relates to your child’s symptoms.