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Diseases > Anti-Nuclear Antibody (ANA) Test

The Anti-Nuclear Antibody (ANA) Test

We all know that every cell in our body contains something called a nucleus. The nucleus is essentially the brain center of the cell. There are lots of different proteins in the nucleus that have many different functions and jobs. Here are some examples – DNA is a protein in the nucleus, RNA is another protein, and there are many enzymes which are proteins. All of these proteins in the nucleus can be targets for an immune attack. The Anti-Nuclear Antibody (ANA) test is a test to see if there are antibodies in the blood that are attacking a protein in the nucleus. The test is a simple screening test. It doesn’t tell you what protein the antibody is attacking it just tells you that there are antibodies against something in the nucleus. Have you ever been fishing? Have you ever used or seen a fish finder? Well, the ANA is really like a fish finder but instead of looking for fish we’re looking for anti-nuclear antibodies. If you use a fish finder you can see down below the water and determine if there are fish down there. You can also get an estimate of just how many fish there are. Now, you don’t know what type of fish they are or what they are doing. They could be benign dumb cod fish just swimming around not bothering anyone or they could be a school of pirrhanas ready to attack. The same is true when we do the ANA test – we can see that there are antibodies but we don’t know what they are directed at or what they are doing. If you think of it this way you get a really good sense of the limitations of the ANA test. The ANA test is really a test of “autoimmunity”. Autoimmune means that the body has failed to recognize its own parts as self, which allows an immune response against its own cells and tissues. By definition, Systemic Lupus Erythematosus is an autoimmune disease. In the case of lupus, the body mounts an immune response to proteins in the nucleus of the cells. Therefore almost everyone (99%) of people with lupus must have a positive ANA. General rule – if the ANA is negative – it ain’t lupus! Remember, if the ANA is negative, it ain’t lupus. One last time – negative ANA – No lupus! If the ANA is positive it could mean other diseases – not just lupus. We can divide ANA diseases into rheumatic and non-rheumatic. We’ll talk about the non-rheumatic diseases below. The other rheumatic diseases where you might see a positive ANA include:

  1. Sjogren’s Syndrome (SS): This is an autoimmune disease which attacks the tissue of salivary glands
  2. Rheumatoid Arthritis (RA)
  3. Systemic Sclerosis (Scleroderma) (SSc)
  4. Inflammatory Myositis (polymyositis and dermatomyositis) (IM)
  5. Overlap or undifferentiated Connective Tissue Diseases: These conditions have features of multiple connective tissue diseases including (RA, SLE, SS, IM, and SSc)
  6. Mixed Connective Tissue Disease (MCTD)

When we start the ANA test we take one part of your serum (the liquid part of blood) and dilute it with 40 parts of a liquid called diluent. Kind of like making frozen orange juice – one can of frozen juice to 4 cans of diluent (which is water). So the serum is diluted to a ratio of 1 in 40. In the lab the technologist looks to see if he or she can see anti-nuclear antibodies at this dilution. If we can the sample is then made half strength from 1 in 40 to 1 in 80. The tech looks again to see if ANA are still present when diluted to 1 in 80. The tech continues this diluting to 1:160, 1:320, 1:640, 1:1280, and finally 1:2560. The lowest dilution is 1:2560. Are you following me? So, why do these titers? What do they mean? If you can still see anti-nuclear antibodies when the serum is diluted to 1 part in 2560 then there must have been a ton of them present in the first place. The reason for diluting like this is that there are 3 things that make ANA dangerous: (1) When there are lots of ANA around (we measure by diluting), (2) When they attach very tightly to the protein (antigen) (we can’t measure this), and (3) What protein (antigen) they are bound to. Diluting only tells us there are lots around. We can’t tell how tightly they attach to the antigen but we can use other tests to help figure out what antigen they’re attacking. However, not all ANA are trouble. We all transiently make ANA. If you go out and corral a group of 100 “so-called” healthy people and do an ANA test, what do you think will be the results? About 30 of them will have an ANA of 1:40, 10 will have an ANA of 1:80, and 3 will have an ANA of 1:160. You see, cells are constantly turning over in our body and during this turnover the nuclear contents may be briefly revealed to the immune system. So it would be normal for the immune system to make an antibody to nuclear contents as the immune system doesn’t normally see them. The problem comes when the immune system can see the nuclear contents for a long time and mount a significant antibody response. Then there are lots of antibodies made. In my time as a rheumatologist I’ve not seen someone with “severe” lupus, one that attacks the organs, when the ANA is low. The titres I really worry about are those at 1:640, 1:1280, and 1:2560. I’m not that concerned at titres of 1:40, 1:80, or even 1:160 because the current ANA tests are just so sensitive. The titre of 1:320 is the cusp as I’m never sure where this one is going to fall.