Wegener’s granulomatosis is diagnosed by:
**Core Concept**
Wegener's granulomatosis, now known as **Granulomatosis with Polyangiitis (GPA)**, is a form of **vasculitis** that affects small- and medium-sized vessels. The diagnosis of GPA involves a combination of clinical, radiological, and pathological findings.
**Why the Correct Answer is Right**
The correct answer is based on the fact that GPA is characterized by the presence of **anti-neutrophil cytoplasmic antibodies (ANCA)**, particularly **c-ANCA** (cytoplasmic ANCA) or **p-ANCA** (perinuclear ANCA), which are detected by immunofluorescence assays.
**Why Each Wrong Option is Incorrect**
**Option A:** Is incorrect because while **biopsy** is important for diagnosis, it is not the only method.
**Option B:** Is incorrect because **chest X-ray** may show abnormalities but is not diagnostic.
**Option C:** Is incorrect because **urine analysis** may show renal involvement but is not specific.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that **ANCA positivity** is a crucial diagnostic criterion for GPA, but it is not exclusive to this condition.
**Correct Answer:** D. ANCA positivity.