Serum Proteinase 3 (PR3) Antigen Level

Why This Test Might Be Ordered

Your healthcare provider may order this test if you have symptoms or risk factors for conditions like vasculitis—a group of diseases that cause inflammation in blood vessels—or if you have an elevated white blood cell count or other signs of inflammation. It may also be used in the evaluation of certain infections or to monitor treatment responses.

What to Expect Before the Test

No special preparation is typically needed for this test. You may have a small needle inserted into a vein in your arm to draw blood. If you’re on blood-thinning medication, let your provider know before the test.

What the Test Results Mean

Results are usually reported as a concentration in micrograms per milliliter (µg/mL). While reference ranges vary by lab, elevated levels may suggest conditions like certain types of vasculitis or autoimmune disorders, while lower levels may be normal or need further evaluation.

Common Conditions Monitored or Diagnosed

PR3 levels are often checked in patients with suspected **granulomatosis with polyangiitis (GPA)**, a type of vasculitis that affects small and medium blood vessels. It can also be used in the evaluation of other inflammatory or autoimmune conditions, such as certain types of vasculitis or autoimmune rheumatic diseases.