Introduction
Autoantibodies are antibodies that react with self-antigens. These antigens may be present on all cell types or highly specific to particular cell types in body organs (thyroglobulin in thyroid cells, etc). They may contain proteins, carbohydrates, lipids, or various combinations thereof. Scleroderma (also called systemic sclerosis) is a group of rare connective tissue diseases. There are two subtypes of systemic sclerosis, defined based on the amount of skin affected -
-
Diffuse systemic sclerosis that affects the whole body
-
Limited systemic dermatosclerosis is typically associated with one or more symptoms collectively referred to as CREST syndrome.
Limited cutaneous systemic sclerosis, which is a subtype of systemic sclerosis, is characterized by cutaneous fibrosis of the fingers (sclerodactyly) and sometimes of the face and neck or the skin on the side of the elbows and knees. It is characterized by fibrosis. The upper arms, thighs, and torso are not affected. Symptoms of CREST syndrome include:
-
Calcification - Deposition of calcium under the skin.
-
Raynaud's Phenomenon - Episodes of decreased blood flow to fingers and toes that turn them white or blue.
-
Esophageal Dysfunction - Difficulty swallowing, acid reflux, chest burn.
-
Telangiectasia - Red patches on the skin caused by swollen capillaries.
-
Sclerodactyly - Shiny, tight and thick skin on the hands and fingers.
What Is Anticentromere Antibody Test?
Anti-centromere antibodies (ACAs) are autoantibodies, proteins produced by the immune system that mistakenly target the body's own tissues. It targets centromeres, the building blocks of chromosomes (structures within the cell nucleus) found in all nucleated cells in the body except red blood cells. The ACA test detects and measures the total amount of anticentromere antibodies present in the blood to help diagnose scleroderma. The ACA test can be ordered with other autoantibody tests, including the ANA (antinuclear antibody) test. The ACA test can be used to give the doctor additional information if the ANA test is positive, especially if the test reveals specific patterns characteristic of certain antibodies.
What Do the Anticentromere Antibody Test Results Mean?
If a positive ACA result is present and an individual is having anticentromere antibodies in the blood, suggesting that symptoms of CREST are present, then an individual probably has limited cutaneous scleroderma. ACA is found in approximately 60 to 80 % of patients with limited cutaneous scleroderma and up to 95 % of patients with CREST syndrome. Approximately five to seven percent of ACA-positive patients develop diffuse cutaneous scleroderma.
If the ACA result is negative, the symptoms may be due to another medical condition. However, although rare, limited cutaneous scleroderma may fail to produce anticentromere antibodies and result in a negative ACA test. Blood levels of ACA can change over time, but once symptoms develop of ACA presence, an individual can continue to produce it for the rest of their life.
How Is the Test for Anticentromere Antibody Conducted?
A two milliliters blood sample is taken for testing for anticentromere antibodies, and a fasting sample is preferred. The doctor will take a blood sample and send it to a laboratory. In the laboratory, the blood will be tested for antibodies. It also measures the levels of certain types of antibodies. The sample is stable for 21 days when refrigerated and kept in serum form. A medical professional uses a small needle to get a blood sample from a vein in the arm. After the needle prick, a small amount of blood is drawn into a test tube or vial. There may be a slight tingling sensation when inserting and removing the needle. Usually, this process takes no more than five minutes.
What Are the Reference Values for Anticentromere Antibody Test?
Antibody levels less than 1.0 U is considered a negative result, and the result more than or equal to 1.0 U is considered a positive result. Reference values apply to all age groups. Anti-centromere antibodies appear early in the disease process and predict particularly limited skin involvement and a reduced likelihood of active involvement of internal organs such as arteries.
Conclusion:
Anti-centromere antibodies are autoantibodies specific for centromere (constricted region in the chromosome) function. They occur in some autoimmune diseases, usually in focal systemic sclerosis (previously called CREST syndrome) and occasionally in diffuse scleroderma. It is rare in other rheumatic diseases and in healthy people. Anti-centromere antibodies are found in approximately 60 % of patients with focal systemic sclerosis and 15 % of patients with diffuse sclerosis. The specificity of this test is over 98 %. A positive anticentromere antibody finding is, therefore, highly suggestive of localized systemic sclerosis. Anti-centromere antibodies appear early in the course of the disease process and are predictive of skin involvement, and a decreased risk of aggressive involvement of internal organs such as fibrosis of the lungs.
