My doctor wanted to start me on methotrexate but I don't like the thought of starting that drug without some sort of definitive diagnosis.
Info from Brighton & Sussex Pathology:
In general in the context of small vessel vasculitis:
C-ANCA is associated with anti-PR3 antibodies and is found in Wegener’s Granulomatosis, and Churg-Strauss Syndrome.
P-ANCA is associated with anti-MPO antibodies and is found in Microscopic Polyangiitis, Crescentic Glomerulonephritis and Churg-Strauss Syndrome.
But this is variable and one may have C-ANCA with anti-MPO and P-ANCA with anti-PR3, or combinations of antibodies.
A positive ANCA with negative anti-MPO and PR3 may be found in a variety of conditions including autoimmune hepatitis, sclerosing cholangitis, ulcerative colitis, SLE, RA, malignancy and chronic infections. ANCA testing is not warranted for these clinical conditions.