The truth about ANAs

in by kbunny82

My blood work came back positive for autoimmune thyroid and an elevated RNP, although my ANA showed negative. I saw a rheumatologist and he stated that you cannot have MCTD if your ANAs show negative. So what is the connection between ANAs and other antibodies such as RNP and is what the rheumatologist stating true?

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1 Answer


I would like to start the answer to this question by stating that laboratory testing never 100% accurate. Lab results are meant to be used in combination with other lab testing, signs and symptoms, and physical exam performed by a physician. Diagnosis should never be made from a single laboratory result.

Mixed Connective Tissue Disease (MCTD), like all of the autoimmune connective tissue diseases, is very difficult to diagnose. There is currently no gold standard for the diagnosis of MCTD, but instead is based off of clinical presentation and the presence of auto-antibodies. Current criteria says that MCTD is most likely present if there are the presence of Anti-RNP antibodies accompanied by 2-3 or more clinical criteria – swollen hands, synovitis (joint swelling), myositis (muscle inflammation), and Raynaud’s phenomenon.

With that being said, antinuclear antibody (ANA) testing is almost always positive in MCTD, and in this case it is a little odd that it would be negative. Anti-RNP antibodies in and of themselves are a type of ANA, so their presence should automatically indicate a positive ANA. The presence of a negative ANA could be caused by number of different things and should be looked into further.

It is possible that the ANA testing is incorrect and that this is a false negative result (meaning that there should really be a positive result recorded). Although this is highly unlikely with this test (ANA testing has been created to have more false positives than negatives), it is not impossible. It is also possible that the anti-RNP testing is a false positive (meaning that it should have been negative but for whatever reason was recorded positive). Another possibility is that there is a positive anti-RNP but the levels are so low that they showed up on the specific RNP testing but not on the overall ANA testing (though this is probably rare).
In the presence of symptoms that are specific with MCTD along with a positive RNP, re-testing of anti-RNP and ANA levels should be considered to verify the previous results. Also keep in mind that any anti-inflammatory or immune suppressing medication may result in a false negative result.

ANA testing looks for very specific antibodies known as antinuclear antibodies. These are most often autoantibodies that are seen in diseases such as lupus, rheumatoid arthritis, scleroderma and MCTD. Although there are correlations between ANAs and other organ autoimmune diseases such as autoimmune thyroiditis, it is not as common to see elevated ANAs in those conditions. Another consideration is that there is often a correlation between autoimmune diseases. Once a particular autoimmune disease has been developed, there is an increased risk of developing another autoimmune response, or to have overlapping symptoms and responses.

Autoimmune diseases can be very difficult to diagnose. They require the careful eye of a physician who looks at the entire presentation of a particular disease. If laboratory testing is confusing or physicians are not clear on their reasoning for a particular diagnosis, then it may be helpful to get a second opinion.

Jenny Bennett, ND LAc

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Answered on January 22, 2014

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