Autoimmune Testing: Anti-Nuclear Antibodies (ANA)
Quick Notes
- ANA stands for Anti-Nuclear Antibodies
- ANA represents a group of various antibodies - all of which attack certain parts of our nuclei (the nucleus is the center or 'brain' of our cells.
- ANA is associated with many autoimmune diseases, but has a very close relationship to the disease Systemic Lupus Erythematosus
Anti-Nuclear Antibodies are one class of antibodies involved in some (but not all) autoimmune diseases. The topic of autoimmune disease testing is a confusing one – this article will shed some light on the concept of ANA and its clinical use and interpretation.
Testing in Autoimmune Disease
We run tests in patients for several reasons: such as confirming a diagnosis, estimating disease severity and aid in assessing the progression of disease activity.
Hallmarks of autoimmune disease include self-reactive T-cells, inflammation and autoantibodies.
Testing is difficult because no one single test has established a definitive diagnostic power. Meaning, a multitude of tests exists, and diagnosis of disease is made with carful interpretation of various tests.
Anti-nuclear antibodies (ANAs) are one class of autoantibodies.
What is an Anti-Nuclear Antibody or ANA
Anti-nuclear antibodies (ANAs) are actually describing a diverse group of antibodies that react against nuclear, nucleolar or perinuclear antigens [1]. The image below shows the basic cell structure, including the nucleus.
Antinuclear antibodies describe various antibodies which attach the nucleus of the cells. They include: [2]
- Anti-RNA antibodies
- Anti-ENA antibodies
- Antinuclear Smith (SM) antibodies
- Antinuclear RNP antibodies
- Antihistidyl antibodies
- Antichromatin antibodies
- Antinucleosome antibodies
- Antihistone antibodies
- Anti-DNA antibodies
- Anti–ds-DNA antibodies
- Anti–ss-DNA antibodies
- Anti–SS-A (Ro)
- Anti–SS-B (La)
The ANA Test
We can test for anti-nuclear antibodies in our blood. It’s called the serum ANA test. This is very useful for screening for autoimmune disease.
ANA test results can be presented in one of 2 ways [1]
- The dilution of serum that tests positive
- The degree of positivity measured by the testing procedure
Many autoimmune diseases are associated with antinuclear antibodies [2]
- Systemic lupus erythematosus
- Sjogren syndrome
- Scleroderma
- Raynaud disease
- Rheumatoid arthritis
- Dermatomyositis
- Mixed connective tissue disease
- Autoimmune hepatitis
- Autoimmune thyroiditis
- Juvenile rheumatoid arthritis
- Primary biliary cirrhosis
- Polymyositis
It should be noted, simply having a positive ANA does not necessarily rule the disease in. Other tests are often run to make the definitive diagnosis. For example, most conditions have other antibodies (more than just the anti-nuclear antibodies), so further testing is crucial.
In the chart below – you’ll see: if a person simply had positive ANA, you can’t really make a diagnosis, all of the diseases below have positive ANA, the other antibodies have to be checked out too!
| AUTOIMMUNE DISEASE | POSTIVE ANTIBODIES |
| SLE | ANA, SLE prep, ds-DNA, ss-DNA, anti-DNP, SS-A |
| Drug-induced SLE | ANA |
| Sjogren syndrome | RF, ANA, SS-A, SS-B |
| Scleroderma | ANA, Scl-70, RNA, ds-DNA |
| Raynaud disease | ANA, Scl-70 |
| Mixed Connective tissue disease | ANA, RNP, RF, ss-DNA |
| Rheumatoid Arthritis | RF, ANA, RANA, RAP |
| Primary biliary cirrhosis | AMA |
| Thyroiditis | Antimicrosomal, antithyroglobulin |
| Chronic active hepatitis | ASMA |
ANA and Lupus
As mentioned above, ANA is associated with many diseases.
ANA hallmarks the diagnosis of Systemic Lupus Erythematosus. In other words, if a person has a negative ANA, we can rule out Lupus [2]. ANA has a very high sensitivity but lacks specificity. Click here to review the concept of test sensitivity and specificity, a very important concept in understanding autoimmune testing.
Summary
ANA’s are simply anti-nuclear antibodies.
They include a group of antibodies which attack various parts of or cells core – the nucleus. Many autoimmune diseases see elevated amounts of ANAs, so we use this blood test as a screening test for autoimmune disease.
If you have positive ANA – it means more testing is necessary. ANA will set you down the proper path. You may also want to read an accompanying article on factors which falsely elevate or lower ANA, available here.
If you test negative for ANA – it also means more testing is necessary. Some autoimmune diseases won’t have positive ANA.
Click here to learn more about testing accuracy by reading about Sensitivity and Specificity. This will help you understand how tests aren’t perfect.
