Fluctuation regarding C-ANCA (PR3) antibodies test results?

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I had some blood test for c-anca (pr3) antibodies and I got intriguing results: in November and December I got posivite results, but in January it was negative. Then, again, in February I got positive results from two different laboratories, with one of them showing 40 and the other one 70. Now, today, the laboratory which gave me the 70 results has been giving me a 92 outcome. As an idea, where I live, for a negative interpretation, the laboratories have taken a minimum or equal to 5 limit.

How can this be possible? I was thinking that either one of the laboratories makes the blood analysis in the wrong way or c-anca jumps from value to value in just a week or two.

I am taking prednisone and cyclophosphamide since November last year after I was considered to be healthy exactly one year ago - and all of this due to a positive c-anca result from November. If there really is a fluctuation, I am thinking about a conspiracy theory against me as my creatinine level is normal and, overall, the rest of the blood test are pretty good (except for proteins which I understood that will never be in the ok limits since the kidneys are affected) smile

What do you folks think? Am I losing my mind here or this happened to any of you? 

Thank you!

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  • Posted

    Paul my son is 12 years old and has the same fluctuations with his PR3. His levels can go from 5.3 up to a 16 or  18. He gets his blood taken every 3 months. All other test are normal.  I don’t understand the fluctuations either. Neither does his rheumatologist. 
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    • Posted

      Sorry to hear about your son, Marva! I hope he is doing well! Is he under treatment? Which parts of the body were affected? 

      I was thinking, as an absurd idea, that even the meds we take have an effect on the outcome result for the c-anca, whether it is positive or negative, it has some influence. Sounds like a paradox, but I did a lot of reading and it seems that prednisone has an effect on different type of blood tests, it can either make them positive or negative. I do not know what to think anymore... 

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  • Posted

    Hi Paul,

    I have had my doctors disagree on what the c-Anca PR3 antibodies test means. My Pulmonary  and Nephrology doctors had the opinion that a positive test for the PR3 antibodies was a marker for my Wegener's being active while my Rheumatologist did not. My Nephrologist was pretty adornment about the numbers then all of a sudden he flipped positions. It was at this point I increased my research and I found the following:

    "The c-ANCA/PR3 antibody test is a helpful diagnostic tool that is used most effectively when patients are thought to possibly have GPA/Wegener’s. A positive test is supportive of the diagnosis.  However, occasionally the test is negative but GPA/Wegener’s is present.  Some physicians use the ANCA test to monitor treatment and disease status.  Test results by themselves do not always indicate that the disease is active, so that physicians cannot use them as the primary guide to decision making about treatment.  Decisions to change treatment should be based on convincing features of GPA/Wegener’s disease activity or remission, and appropriate laboratory tests including urinalysis"

    For more information ,here is the link


    After showing this document to my Pulmonary doctor, he too became less concerned about the PR3 numbers.

    My research also found that when the PR3 number is above 8, the results become non-linear and may not have much meaning.

    The bottom line is to not put too must weight on the PR3 number. I too have had the C-Anca test came back negative and then several months later had a number over 70. 


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    • Posted

      Hello Melvin,

      Thank you for your input! I have read before about the C-Anca test about not being 100% conclusive in putting a diagnostic. This is where the problem rises for me: not knowing what do next. I would quit the meds in an instance, but I am not sure whether the test shows an active diseases or not. I feel like I am taking the medicine for nothing, for something that does not exist. It is crazy as I am feeling good, I am careful with what I eat, I try to do exercises whenever I can and be active... 

      Even if I were to go to another doctor, I am sure that whatever opinion he may have, it will still be questionable as it seems that nothing is decisive.

      I hope you are doing well and everything is ok with you! 

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