Anti Nuclear Antibody, EIA
What is ANA?
The anti nuclear antibody (ANA) test is used to detect the presence of antinuclear antibodies (ANA) in blood. ANAs are antibodies that cause disease by attacking healthy cells and tissues. The ANAs can cause damage to the joints, skin, muscles, and many other parts of the body. This test is suggested for people at risk or having autoimmune disorders such as rheumatoid arthritis, autoimmune hepatitis, scleroderma and systemic lupus erythematosus (SLE).
Most people have a minor percentage of ANA in their blood but having too much of it can be a sign of an autoimmune disease. The ANA levels also tend to increase with certain medications and age. A positive ANA test alone can’t diagnose a specific disease, further testing is also needed to know the underlying cause.
Why is ANA done?
· To determine the presence of an autoimmune disease like Systemic Lupus Erythematosus (SLE)
· To evaluate the possible presence of autoimmune Connective Tissue Disorders (CTDs) other than SLE such as Polymyositis, Scleroderma, Sjögren's syndrome etc.
What does ANA Measure?
Antinuclear antibody (ANA) test screens for the presence of ANA in blood. The immune system of the body is responsible for differentiating between the body’s own cells and foreign cells, like pathogens. Once the foreign cells are identified, they are then targeted and destroyed. In autoimmune disorders, the immune system of the body is unable to recognize certain cells as the body’s own cells and starts an immune response against them which results in their destruction. The recognition of ‘self’ and ‘non-self’ cells is mediated by certain proteins present on the surface of cells or inside them. When the immune system identifies a cell as foreign or ‘non-self’, it produces antibodies against these cells to destroy them. Antibodies produced in an autoimmune disease are called autoantibodies.
Antinuclear antibodies (ANA) are autoantibodies that are produced against protein markers present in the nucleus of certain cells of the body. They are produced in a number of autoimmune diseases but are most commonly produced in Systemic Lupus Erythematosus (SLE).
The Antinuclear Antibody Test can be performed either by Immunoassay method (ELISA) or Indirect Fluorescent Antibody (IFA) method to detect ANA in blood. Both these tests may be used by some laboratories together: the Immunoassay method (ELISA) screens for the presence of antinuclear antibodies, and IFA method subsequently confirms the positive or equivocal Immunoassay results.
ANA by Immunoassay method (ELISA) utilizes a mixture of known anti-nuclear antigens and is fairly simple to perform, can be automated and provides fairly objective results.
Interpreting ANA results
Results are provided as positive/negative or with an index value against a cutoff value.
A positive ANA test can also be seen in healthy individuals, particularly the elderly or in diseases other than Connective Tissue Disorders (CTD), where it has no diagnostic value.