What is the role of lab tests in the workup of granulomatosis with polyangiitis (GPA)?

Updated: Aug 31, 2021
  • Author: Christopher L Tracy, MD; Chief Editor: Herbert S Diamond, MD  more...
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Routine laboratory tests are nonspecific in granulomatosis with polyangiitis (GPA). Elevated blood urea nitrogen (BUN) and creatinine levels may signal renal involvement. Hypoalbuminemia may be present. Serum complement levels are within the reference range or increased. [55]

Mild normochromic normocytic anemia is present in 50% of patients. A peripheral blood smear may show schistocytes and burr cells. Leukocytosis is also common, with a neutrophil predominance. Eosinophilia is not a feature of GPA but rather of allergic granulomatous angiitis (Churg-Strauss syndrome).

Westergren erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels are elevated in 90% of patients with active and generalized disease. They may decrease in response to treatment.

In patients with renal involvement, urinalysis may show non-nephrotic–range to nephrotic-range proteinuria, microscopic hematuria, and the presence of red blood cell (RBC) casts consistent with underlying glomerulonephritis.

Rheumatoid factor is positive in a low titer in two thirds of patients, whereas antinuclear antibody is present in 10-20% of patients. Hypergammaglobulinemia may be present.

Whether tissue diagnosis is always required for GPA remains controversial. As the therapy for severe GPA is not benign, tissue diagnosis is recommended if a biopsy site is available, provided that the patient understands the risks of the procedure.

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