Among the laboratory results at diagnosis, white blood cell count, and blood urea nitrogen levels in PR3-ANCA-positive MPA patients were significantly lower than PR3-ANCA-negative patients (6,700 vs. 8,700/mm3, P = 0.035, and 13.8 and 20.4 mg/dL, P = 0.043, respectively). Here, PRTN3 is linked to microscopic polyangiitis.