occur in more than 90% of patients with systemic Wegener's granulomatosis (with renal or pulmonary involvement, or both), 75% of patients with limited Wegener's granulomatosis (without renal involvement) and 50% of patients with microscopic polyarteritis.
c-ANCAs are actually antibodies to protein 3. The presence of c-ANCAs is 98% specific for these diseases;
changes in c-ANCA levels often precede disease activity and may guide treatment.
a primary care physician will rarely need to order this test
it helps in the diagnosis and management of only a very small number of patients with relatively rare conditions, and screening patients with nonspecific symptoms results in many false-positive p-ANCA results