Antinuclear Antibody (ANA) Test

The Antinuclear Antibody (ANA) test is a blood test used to diagnose and monitor autoimmune disorders, particularly Systemic Lupus Erythematosus (SLE). The test detects the presence of antinuclear antibodies in the blood, which are proteins that attack the body's own tissues.

What are Antinuclear Antibodies?

Antinuclear antibodies are a type of autoantibody that targets the cell nucleus, which contains the genetic material. In healthy individuals, the immune system produces antibodies to fight off foreign substances, such as viruses and bacteria. However, in people with autoimmune disorders, the immune system mistakenly produces antibodies against the body's own tissues, including the cell nucleus.

How is the ANA Test Performed?

The ANA test involves a blood draw, where a sample of blood is taken from a vein in the arm. The blood sample is then sent to a laboratory for analysis. The test uses a technique called indirect immunofluorescence, which involves adding the patient's serum to a slide containing human tissue culture cells or mouse liver cells. If antinuclear antibodies are present, they will bind to the cell nuclei and can be visualized using a fluorescent dye.

What do the Results Mean?

The results of the ANA test are reported as a titer, which indicates the level of antinuclear antibodies in the blood. A positive result is typically defined as a titer of 1:80 or higher. However, the interpretation of the results depends on the clinical context and the presence of other symptoms.

• A low titer (1:80 to 1:160) may be seen in healthy individuals or those with non-autoimmune disorders.
• A moderate titer (1:320 to 1:640) may indicate an autoimmune disorder, such as SLE or rheumatoid arthritis.
• A high titer (1:1280 or higher) is more likely to be associated with an autoimmune disorder, particularly SLE.

What are the Limitations of the ANA Test?

The ANA test has several limitations. A positive result does not necessarily mean that a person has an autoimmune disorder, as antinuclear antibodies can be present in healthy individuals or those with non-autoimmune disorders. Additionally, a negative result does not rule out an autoimmune disorder, as some people with SLE or other conditions may have a negative ANA test.

When is the ANA Test Ordered?

The ANA test is typically ordered when a healthcare provider suspects an autoimmune disorder, such as:

• Systemic Lupus Erythematosus (SLE)
• Rheumatoid arthritis
• Scleroderma
• Sjögren's syndrome
• Polymyositis or dermatomyositis

The test may also be ordered to monitor the effectiveness of treatment for an autoimmune disorder or to check for potential side effects of certain medications.