Renal vasculitis occurs in the setting of autoimmune inflammation of small blood vessels - Wegener granulomatosis, Churg-Strauss syndrome, and microscopic polyangiitis. Rapidly progressive and/or necrotizing glomerulonephritis are the histopathological hallmarks of this condition, with main manifestations being proteinuria and hematuria. The diagnosis requires laboratory workup and biopsy.
Renal vasculitis may develop in patients suffering from vasculitis affecting smaller vessels, as is the case in ANCA-associated vasculitides (ANCA means antineutrophil cytoplasmic antibody)  . Wegener granulomatosis, microscopic polyangiitis (MPA), and Churg-Strauss syndrome (also known as eosinophilic granulomatosis with polyangiitis) are described as potential causes of renal vasculitis. The clinical presentation of these diseases, although varying in terms of non-renal manifestations, have similar features regarding the kidneys. Hematuria and proteinuria, as well as the presence of white blood cells, casts, and crystals in urine sediment are typical findings . Acute kidney injury (AKI), defined as a rapid decrease in kidney function causing azotemia and electrolyte disbalance, is frequently encountered in patients who develop rapidly progressive glomerulonephritis (RPGN), which is a typical lesion seen in more severe renal injury due to autoimmune mechanisms. In most severe cases, end-stage renal disease (ESRD) due to RPGN may occur in a very short time span, especially in absence of a prompt and accurate diagnosis . Despite the fact that large and medium-sized vessels vasculitic syndromes (such as Takayasu and Kawasaki arteritis, polyarteritis nodosa, and giant cell arteritis) rarely cause glomerulonephritis, these diseases are important causes of renal vasculitis as well  .
To make the diagnosis of vasculitis, it is necessary to obtain a thorough patient history and conduct a detailed physical examination. If hematuria is noted, parameters of kidney function - creatinine, blood urea nitrogen (BUN), and serum electrolytes should be evaluated . Furthermore, determination of proteinuria, as well as the presence of red and white blood cells, casts, and crystals can be achieved by simple urine testing and are valid indicators of glomerular damage . Detection of anti-neutrophil cytoplasmic antibodies (both perinuclear and cytoplasmic, or p-ANCA and c-ANCA, respectively) in serum may be of a great help in making the diagnosis of small vessel vasculitis, but large titers are observed in all cases of ANCA-associated vasculitides, necessitating additional procedures to confirm the underlying disease . Ultrasonography, computed tomography (CT), and magnetic resonance imaging (MRI) can be used as adjunctive procedures, but the use of a contrast needs to be avoided, as further damage to the kidneys may occur . Fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) is an important imaging study if solid clinical suspicion of vasculitis exists, mainly because it shows which organs are affected by vasculitis . To confirm the diagnosis, the kidney biopsy is the gold standard . Segmental fibrinoid necrosis, an absence of immune deposits in the glomeruli (as seen in pauci-immune glomerulonephritis), and the presence of glomerular crescents are frequently present in ANCA-associated glomerulonephritis  .