What diagnostic test is used to confirm Wegener's granulomatosis?

Wegener's granulomatosis, now more commonly referred to as granulomatosis with polyangiitis (GPA), is a type of vasculitis that primarily affects the respiratory tract and kidneys. The diagnosis of this condition is confirmed through a combination of specific laboratory tests and tissue examination.

C-ANCA (cytoplasmic anti-neutrophil cytoplasmic antibodies) is a key serological marker that is often found in patients with GPA. The presence of these antibodies strongly suggests the diagnosis of granulomatosis with polyangiitis. Importantly, a tissue biopsy showing granulomatous inflammation or necrotizing vasculitis from an affected organ (such as the lungs or kidneys) further corroborates the diagnosis. Hence, both the serological testing for C-ANCA and the histological confirmation via biopsy are integral to establishing the diagnosis of this condition.

While urinalysis can provide subclinical evidence of renal involvement (such as hematuria or proteinuria), and a CT scan can help visualize pulmonary nodules or infiltrates, these methods do not confirm the disease itself. Blood cultures are not relevant for the diagnosis of Wegener's granulomatosis, as this condition is not caused by an infectious