The FAN test is a type of test widely used to aid in the diagnosis of autoimmune diseases, especially Systemic Lupus Erythematosus (SLE). Thus, this test aims to detect the presence of autoantibodies in the blood, which are antibodies produced by the body and that attack its own cells and tissues.
This exam is based on the fluorescence pattern of antibodies, being possible to visualize under the microscope and help in the diagnosis of several diseases. Although it is normal to have a low ANA test result, when this number is very high, it can mean that there is an autoimmune disease that needs to be identified and treated as soon as possible to alleviate the symptoms.
what is it for
This FAN exam can help diagnose autoimmune diseases such as:
- Lupus, which is an autoimmune disease characterized by inflammation of the joints, skin, eyes and kidneys, for example;
- Rheumatoid arthritis, in which there is pain, redness and swelling of the joints.
Blood collection is usually done at the hospital, but it can also be done in specialized clinics, both for adults and children. In the case of babies, the collection is usually made with a small prick on the foot, without the need to use a needle.
In the laboratory, the test is carried out by adding a fluorescent dye labeled with the antibodies to be identified to the sample. The dye-labeled blood is then placed in a container containing a human cell culture known as Hep-2 cells, which allows clear visualization of various cell structures and cell cycle phases. Thus, it is possible to make the diagnosis, as it is made from the fluorescence pattern observed through the microscope.
What preparation is needed
There is no special preparation for the FAN exam, it is only recommended to inform the doctor about the medication being used and possible health problems.
what the results mean
In healthy people, the FAN exam is usually negative or non-reactive, presenting values such as 1/40, 1/80 or 1/160. However, this does not mean that whenever it is negative there is no autoimmune disease. Thus, even if it is negative, and according to the symptoms presented, the doctor can order other tests to confirm that it is not an autoimmune disease.
When the result is positive, or reactive, it usually presents values of 1/320, 1/640 or 1/1280. In addition, there is also the positivity pattern that is based on the fluorescence seen under the microscope, which helps to better distinguish the type of disease and which may include:
- homogeneous nuclear: may indicate the presence of lupus, rheumatoid arthritis or juvenile idiopathic arthritis, depending on the antibody identified. If the presence of anti-DNA, anti-chromatin and anti-histone antibodies is identified, it is indicative of lupus;
- Centromeric dotted nuclear: normally indicative of scleroderma;
- fine dotted nuclear: usually indicates Sjögren’s syndrome or lupus, depending on the antibody identified;
- thick dotted nuclear: lupus, rheumatoid arthritis or systemic sclerosis according to the identified antibodies;
- fine speckled cytoplasmic: can be polymyositis or dermatomyositis;
- continuous nuclear membrane: may indicate autoimmune hepatitis or lupus;
- dotted nucleolar: this is usually a sign of systemic sclerosis.
These results should always be interpreted and evaluated by a physician, and in almost all cases further testing is required before confirming the diagnosis.