Anti-MPO antibodies

The anti-MPO test measures antibodies your immune system may produce against myeloperoxidase, an enzyme found inside certain white blood cells. These antibodies are one type of antineutrophil cytoplasmic antibody and are often referred to as MPO-ANCA.

Clinicians use this test to help evaluate suspected ANCA-associated vasculitis, a group of conditions that cause inflammation of small blood vessels. It is commonly ordered together with anti-proteinase 3 testing and is performed using immunoassay methods on a blood sample.

Finding anti-MPO antibodies can support the diagnosis of ANCA-associated vasculitis and can help classify the type, which can guide treatment decisions and follow-up. Doctors may order this test if you have signs of small vessel inflammation such as unexplained kidney problems, coughing up blood, persistent sinus or lung issues, nerve pain, or certain skin findings.

A result must be interpreted in the context of your symptoms, examination, and other tests. Anti-MPO antibodies can occasionally be present with other autoimmune conditions, chronic infections, or after exposure to certain medications, so a positive result does not by itself confirm disease. Sometimes a tissue biopsy is needed to make a clear diagnosis.

A positive anti-MPO result suggests your immune system is reacting to myeloperoxidase, which can be consistent with an autoimmune process affecting small blood vessels. A negative result lowers the likelihood but does not fully exclude this group of diseases, especially if your symptoms are strongly suggestive.

Your clinician may look at patterns over time, other antibody tests, urinalysis, kidney function tests, imaging, and sometimes biopsy to clarify what is happening. If a drug exposure is suspected, your care team may discuss changing or stopping that medicine. Talk with your clinician about what your specific result means and the best next steps for you.