Antinuclear antibodies (ANA) are proteins found in the bloodstream of some people who have RA or other diseases. Doctors test for these antibodies to help make a diagnosis of RA and other autoimmune diseases such as systemic lupus erythematosus (SLE) and drug-induced lupus. An ANA test may also be positive in cases of scleroderma, Sj?gren's syndrome, Raynaud's disease, juvenile chronic arthritis, antiphospholipid antibody syndrome, autoimmune hepatitis, and many other autoimmune and non-autoimmune diseases.
Antinuclear antibody (ANA)
An unusual antibody that is directed against structures within the nucleus of the human cell. ANAs are found in patients whose immune systems are predisposed to cause inflammation against their own body tissues.
An antibody is part of the normal human immune system. The body uses such proteins to fight off infections caused by bacteria, viruses, and other infectious agents. Whereas the typical antibodies bind to foreign material (e.g., bacterial cell walls), antinuclear antibodies act somewhat differently: They bind to structures within the center of the person's own cells. The center, or innermost core, of the cell is called the nucleus. It contains DNA along with other genetic material.
ANAs are found in patients whose immune systems may be predisposed to instigate inflammation against their own body tissues. Such antibodies, which are directed against a person's own tissues, are referred to as auto-antibodies. Thus ANAs are a sign of an autoimmune illness. When a person has an autoimmune disease, the immune system produces antibodies that attach to the body's own cells as though they were foreign substances, often causing them to be damaged or destroyed. Both RA and Crohn's disease (an inflammatory bowel disease) are examples of autoimmune diseases. A thorough medical history, physical examination, and other tests besides an ANA test are needed to confirm the diagnosis of a suspected autoimmune disease.
The ANA test is performed using a small sample of blood usually taken from your arm. In traditional laboratory ANA testing, your blood serum is placed in a container with specially grown human cells. If your blood contains antibodies to the tissues in a human cell, they will stick to the cells in the container and can be detected using certain chemicals and a special microscope. Newer, more rapid laboratory techniques are also commonly used to confirm the presence of ANAs. Regardless of which technique is used, the laboratory measures two characteristics of the ANA in your blood: the amount of antibody and the pattern (what the antibody sticks to in the cell).
The amount of antibody is measured by a titer, which indicates how many times the technician could dilute the patient's blood and still detect the presence of ANAs. A titer of 1 to 80 (1:80) means that antibodies could be last detected when 1 part of the blood sample was diluted by 80 parts of another liquid (usually a dilute salt solution). A larger second number indicates that the antibodies are present in greater concentration. For example, a titer of 1:320 indicates a higher concentration of antibodies in the blood than a titer of 1:80, because it took 320 dilutions to get to an undetectable amount of ANA in the former sample versus 80 dilutions in the latter sample. Given that each dilution involves doubling the amount of test fluid, it is not surprising that titers increase rapidly. In fact, the difference between titers of 1:160 and 1:320 is only a single dilution, so it doesn't necessarily represent a major difference in disease activity. Such variability is very common, especially if more than one laboratory is involved in processing the samples.
The amount of ANA in your bloodstream will inevitably go up and down during the course of the disease. For this reason, physicians don't consider the ANA titers to be an accurate reflection of disease activity. A titer of 1:80 or lower is usually considered to be a negative test result.
When looking for the ANA pattern, the technician examines a specially prepared slide under a microscope. ANAs can present as four different “patterns” depending on where the antibodies adhere to the cell nucleus: homogeneous (diffuse), speckled, nucleolar, and peripheral (rim). While these patterns are not specific to any one illness, certain illnesses are more frequently associated with one pattern or another. Thus the patterns can sometimes give the doctor further clues about the types of illnesses to look for when evaluating a patient. For example, the nucleolar pattern is more commonly encountered in scleroderma, the rim (peripheral) pattern is the most specific pattern for lupus, and the homogeneous (diffuse) pattern is the most common pattern seen overall. The speckled pattern is seen in many conditions and in persons who have no autoimmune disease at all.