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ANA Test


ANA stands for Antinuclear Antibody. This literally means 'substance against the cell nucleus'. The nucleus is the 'headquarters' of the living cell, therefore the ANA can damage or destroy cells & tissues.

95%-98% of patients with SLE will have a positive ANA test, but the majority of people with a positive ANA test do not have SLE. A positive ANA test can be found in many conditions, including Sjogren's Syndrome, scleroderma, rheumatoid arthritis, & mixed connective tissue disease. Many normal healthy people will also have a positive ANA test. Therefore a positive ANA test, on it's own, does not mean that person has lupus.

Because of this, the physician has to look very carefully at the titer (number) & pattern of the ANA test. The titer shows how many times the technician had to mix fluid from the patient's blood to get a sample free of ANAs. Thus a titer of 1:640 shows a greater concentration of ANA than 1:320 or 1:160, since it took 640 dilutions of the plasma before ANA was no longer detected. The apparent great difference between various titers can be misleading. Since 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 & 1:320 is only a single dilution. And it doesn't necessarily represent a major difference in disease activity.

ANA titers go up & down during the course of the disease, & may or may not reflect disease activity. Therefore it is not always possible to tell from the titer how severe a person's lupus is.

A titer of 1:80 or lower is usually considered negative.

The pattern of the ANA is studied by microscope. The technician examines a specially prepared slide that shows where antibodies attack the nucleus. Certain antibodies attack certain areas of the nucleus, producing four specific patterns.

The rim (peripheral) pattern is the most specific pattern for lupus, while the homogeneous (diffuse) pattern is the most common pattern seen. The remaining patterns are the speckled and nucleolar patterns. In some cases the pattern helps the doctor decide which of the autoimmune diseases is causing the problem and which treatment program is appropriate.

Because a positive ANA test can be found in other diseases as well as SLE, the physician will use a positive ANA test as only one factor in determining whether or not a patient has lupus. A positive ANA test does not mean that a person has lupus. The physician needs to find other clinical features such as butterfly rashes, arthritis, pleurisy, blood abnormalities, kidney disease, etc., in addition to a positive ANA test before making a diagnosis of SLE.

The reliability of the ANA test depends upon the laboratory. Many variables can interfere with the test & give false numbers. The accuracy of the test can also vary, depending on many factors, such as the strength of the fluorescent antibody, or even the quality of the microscope used.

Once a patient is found to be ANA positive, the physician may want to further investigate which antigen in the nucleus is responsible for the positive ANA test. The knowledge of which antigen is responsible for the positive ANA test can sometimes be helpful in determining which disease is present. For instance, antibodies to DNA (the protein that makes up the body's genetic code) are found primarily in SLE. Levels of these antibodies in the blood can be useful to the physician in following the course of lupus, especially in patients with kidney disease. Anti-DNA levels, however, do not always perfectly match the clinical course of lupus kidney disease. Antibodies to histones (DNA packaging proteins) may be very helpful in determining whether a patient has drug-induced lupus. These antibodies may be found in SLE as well. Antibodies to Sm antigen are found almost exclusively in lupus, & when present, help to clinch the diagnosis of SLE. Antibodies to RNP (ribonucleoprotein) are found in a variety of connective tissue diseases. When present in very high levels, they are indicative of mixed connective tissue disease, a condition with features of SLE, polymyositis, and scleroderma. Antibodies to SS-A are found in both lupus and Sjogren's syndrome and are sometimes associated with babies who are born with neonatal lupus.




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