How is microscopic polyangiitis (MPA) diagnosed?
Suspicion for MPA is based on information gathered from a variety of sources, including:
- Medical history to look for the presence of MPA symptoms
- Physical examination to detect sites of organ involvement and to exclude other illnesses that may have a similar appearance
- Blood tests to look for sites of organ involvement and testing for antineutrophil cytoplasmic antibodies (ANCA)
- Urinalysis to detect excessive protein or the presence of red blood cells
- Imaging tests such as x-rays, computed tomography (CT) or magnetic resonance (MR) scans, which can show abnormalities in affected areas such as the lungs
A positive blood test for ANCA can support a suspected diagnosis of MPA. However, the blood test does not by itself prove the diagnosis of MPA or determine disease activity.
Once the diagnosis of MPA is suspected, a biopsy (tissue sample) of an affected area is often performed to try to confirm the presence of vasculitis. Biopsies are only recommended for organ sites in which there are abnormal findings present by examination, laboratory tests, or imaging.