It can be divided into three major categories: 1. Pre-renal: it refers to ARF caused by insufficient blood supply to the kidney and reduced effective perfusion to the renal parenchyma, but at this time, the renal tissue has not yet undergone organic damage. 2. Post-renal: it refers to ARF caused by urinary tract obstruction. 3. Renal: ARF caused by various renal tissue lesions. Renal ARF can be divided into six types according to the main lesion sites: tubular ARF (e.g., acute tubular necrosis), interstitial ARF (e.g., acute interstitial nephritis), glomerular ARF (e.g., acute nephritis or severe acute nephritis), and renal vascular ARF (including renal small-vessel vasculitides, such as microscopic polyangiitis and Wegener’s granulomatosis, and renal microvascular diseases, such as hemolytic uremic syndrome, etc.). These four ARFs are the most common. ARF due to acute renal cortical necrosis and acute renal papillary necrosis are less common.