ANA tests identify autoantibodies in the body. And, they are one of the tools that clinicians use to help diagnose lupus.
Rheumatologists review laboratory tests, symptom logs, and family history before making a lupus diagnosis. This can be a long and challenging process. ANA tests are a crucial element as they offer insight into the functioning of the immune system by measuring the presence of particular proteins in the blood.
The newest criteria for determining a lupus diagnosis was established by the American College of Rheumatology (ACR) and the European League Against Rheumatism (EULAR) in 2018. The first requirement of the criteria to be diagnosed is:
- Positive ANA test with a titer of at least 80
The titer value relates to the ratio of blood serum being tested to a dilution agent. So, a titer of 80 would mean that for every 80 parts of dilution, there was one part of blood serum. The higher the dilution, the more antibodies would need to be in the blood sample to return a positive result for the test.
What are Antinuclear Antibodies (ANA)?
Before jumping to antinuclear antibodies, we will start with antibodies. Antibodies are proteins made by your immune system that help your body recognize and fight harmful substances, such as bacteria and viruses, by activating the immune system to target them. You can think of antibodies as the soldiers that protect your body from bad, foreign invaders.
Sometimes, antibodies mistakenly attack healthy cells and tissues in the body. This is known as an autoimmune response. Antibodies that target healthy proteins specifically in the nucleus of your cells are called antinuclear antibodies (ANA). To continue the analogy from above, ANAs are rogue soldiers that misidentify the cells they are supposed to ignore, and attack them in error.
NOTE: Most people have some ANA, but having too many of these proteins puts you at an increased risk for developing an autoimmune disease, such as lupus.
Who Gets ANA Tests?
Typically, an ANA test is ordered when someone has symptoms that may indicate a systemic autoimmune disease. Some examples of symptoms that may prompt a doctor to order the test include (but are not limited to):
- low-grade fevers
- arthritis-like pain
- muscle pain
Even with a positive ANA test result, it is not clear that a person has lupus. A study published in 2003 in the New England Journal of Medicine found that 88% of people (115 out of 130) eventually diagnosed with lupus had received a positive autoantibody lab result multiple years prior to the diagnosis. On average, that positive test result occurred 3.3 years before the diagnosis was confirmed.
Quick Stats on ANA Tests and Lupus
- 97% of people with lupus will have a positive ANA test.
- Between 5-20% of the general population will have a positive ANA test. A positive test can be a false-positive, or indicate other conditions, such as thyroid disease, certain liver conditions, or other autoimmune diseases.
What Should I Know About ANA Tests and Lupus?
- There is no one definitive test for lupus – an ANA test is just one tool used to help diagnose lupus.
- The ANA test is not a specific test for lupus. This means that most people with lupus will have a positive ANA test, but not everyone with a positive ANA test has lupus.
- Some medications can produce a positive ANA test, so be sure to tell your doctor about any prescription or over-the-counter drugs you take.
- Test results can fluctuate over time and when they are performed at different labs. However, if you have active lupus, your ANA test will probably be positive at most labs, most of the time.
How is an ANA Test Performed?
- An ANA test is performed in a laboratory, using a sample of your blood.
- The test shows if your immune system is producing antinuclear antibodies. A positive ANA test means antinuclear antibodies are present.
- The most common strategies used for detecting and measuring ANAs are indirect immunofluorescence and enzyme-linked immunosorbent assay (ELISA).
What Should I Do if My ANA Test is Positive?
- Your doctor will interpret your ANA test in the context of your symptoms, other lab work, and your medical history, including family history. Keeping a symptom journal or using digital tools can help you be better prepared to go over your symptoms with your doctor.
- Remember, a single positive ANA does not mean you have an autoimmune disease. And a positive ANA test does not require immediate treatment. Your lupus treatment team will take the ANA test results in context with many other factors.