Pyelonephritis is an upper urinary tract infection caused by a bacterial infection, leading to an inflammatory response in the urinary system. The severity of this condition can vary. Nephritis, on the other hand, refers to the sterile inflammation within the glomeruli of the kidney, which also varies in severity. Therefore, it is challenging to compare these two diseases in terms of their severity. In the case of pyelonephritis, most conditions are relatively more treatable, and using antibiotics can control acute pyelonephritis. However, a small number of patients may develop severe complications such as perinephric abscess, acute renal failure, renal papillary necrosis, and even death from septic shock. The severity of nephritis also varies, with symptoms ranging from significant proteinuria to mild hematuria. Therefore, a comparison should be based on the specific conditions of the patients. (The use of medications should be under the guidance of a doctor.)