The ANA test is the anti-nuclear antibody test. It is used for several diseases, but I will talk to you about its use in Lupus testing.
The antibodies your body makes against its own normal cells and tissues play a large role in lupus. Many of these antibodies are found in a panel, or group, of tests that are ordered at the same time. The test you will hear most about is called the ANA test. This is not a specific test for lupus, however. But, many Lupus patients have a positive ANA
Antinuclear antibodies (ANA) are antibodies that connect, or bind, to the nucleus -- the "command center" -- of the cell. This process damages, and can destroy, the cells. A positive ANA test will confirm a diagnosis of lupus when used in conjunction with other tests, symptoms, and medical history. However, a positive ANA test result does not always mean you have lupus. The ANA can be positive in people with other illnesses, or positive in people with no illness. The ANA can also change from positive to negative, or negative to positive, in the same person. Still, lupus is usually the diagnosis when these antinuclear antibodies are found in your blood.
To perform the ANA (antinuclear antibody) test, a blood sample is drawn from and sent to the lab for testing. Serum from your blood specimen is added to microscope slides which have commerically prepared cells on the slide surface. If your serum contains antinuclear antibodies (ANA), they bind to the cells (specifically the nuclei of the cells) on the slide.
A second antibody, commercially tagged with a fluorescent dye, is added to the mix of your serum and the commercially prepared cells on the slide. The second (fluorescent) antibody attaches to the serum antibodies and cells which have bound together. When viewed under an ultraviolet microscope, antinuclear antibodies appear as fluorescent cells. If fluorescent cells are observed, the ANA (antinuclear antibody) test is considered positive. If fluorescent cells are not observed, the ANA (antinuclear antibody) test is considered negative.
A titer is determined by repeating the positive test with serial dilutions until the test yields a negative result. The last dilution which yields a positive result (flourescence) is the titer which gets reported. The titer shows how many times the technician had to mix fluid from the your 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. Since each dilution involves doubling the amount of test fluid, the titers do increase rapidly. In fact, the difference between titers of 1:160 and 1:320 is only a single dilution. And it doesn't necessarily represent a major difference in disease activity.
Lower than 1:20 is considered a negative result.
1:80 is considered a "low positive" and more tests should be ordered. 95% of people with 1:80 ANA do not have Lupus.
1:160 is considered positive and if SED rates and Complement tests are positive, Lupus is considered.
1:320 is a definite positive and mean the disease is active.
1:640 is considered very high and tissue damage is imminent.
Your titer of 1:640 means that it took many dilutions and is considered a very high number. Your doctors will probably want to run other tests in order to confirm a specific disorder.
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