American College of Rheumatology: 88% sensitivity and 92% specificity for ≥2 criteria
Nasal or oral inflammation
Abnormal chest radiograph showing nodules, fixed infiltrate, or cavities
Abnormal urinary sedimentation (microscopic hematuria)
Granulomatous inflammation on biopsy of an artery or perivascular area
Definitive diagnosis: Biopsy
ANCA +, RF+
CBC: Leukocytosis, normochromic anemia, thrombocytosis
ESR/CRP elevated
BUN/Cr
Urinalysis (hematuria, proteinuria)
CXR- Pulmonary infiltrates and nodules
CT chest
Consider ANA, C3 or C4, cryoglobulins, hepatitis serology, HIV, LFTs, blood culture to rule out other pathology
Other tests: Bronchoscopy, PFT, sinus CT
Granulomatosis with polyangiitis
Polyarteritis nodosa, Eosinophilic granulomatosis with polyangiitis 
Polyarteritis nodosa
Lymphoma, lung cancer
Thromboangiitis obliterans
Pneumonia, infective endocarditis, HUS
Eosinophilic granulomatosis with polyangiitis
Glomerulonephritis