Anti-PR3

Anti-PR3 is a blood test that measures antibodies directed against proteinase 3, an enzyme found inside certain white blood cells called neutrophils. These antibodies belong to a group known as antineutrophil cytoplasmic antibodies. The test is typically performed on a serum sample using an immunoassay.

Anti-PR3 is part of the evaluation for suspected small vessel vasculitis. It is often ordered together with anti-MPO and, when appropriate, an ANCA immunofluorescence test to provide a fuller picture of your immune activity.

Anti-PR3 can help your healthcare team evaluate conditions such as granulomatosis with polyangiitis and related forms of ANCA-associated vasculitis, especially when symptoms involve the sinuses, lungs, kidneys, skin, or nerves. It may be used at diagnosis to document your antibody status and, in selected situations, to support assessment during follow-up.

Results are interpreted together with your symptoms, examination, urinalysis, imaging, and other labs. Anti-PR3 is not exclusive to a single disease and can occasionally appear with other inflammatory conditions or medication exposures, so context is essential to avoid misinterpretation.

A detectable anti-PR3 result increases the likelihood of ANCA-associated vasculitis in the right clinical setting, but no single test confirms or excludes the diagnosis on its own. Some people with active disease can have negative results, and some without vasculitis can have positive results. Your clinician will consider the full picture, including organ involvement and other test findings, before recommending next steps.

For people already diagnosed, changes in anti-PR3 levels may or may not mirror disease activity. Treatment decisions are based primarily on symptoms, organ function, and objective findings. If your result is positive, ask your clinician about additional evaluation, which may include repeat testing, urine and kidney assessments, chest or sinus imaging, or referral to a rheumatologist or other specialists.