Fever of more than 37 degrees in patients with urinary tract infections suggests a high likelihood of pyelonephritis. Urinary tract infection is divided into upper urinary tract infection and lower urinary tract infection. Pyelonephritis is an upper urinary tract infection. Pyelonephritis is often characterized by fever, chills, accompanied by obvious low back pain, pressure pain at the ureteral point and/or cribriform ridge point, and renal tenderness, with or without urinary tract irritation (urinary frequency, urgency, and urinary pain). In addition to the above manifestations, the presence of the following suggests pyelonephritis: positive urine culture after bladder irrigation, i.e., urine bacterial culture colonies are all >10⁵/ml; urine sediment microscopy with leukocyte tubular pattern and exclude interstitial nephritis, lupus nephritis and other diseases; and the manifestation of renal tubular insufficiency. Fever is only one of the symptoms of pyelonephritis, the diagnosis of pyelonephritis still needs to be combined with other symptoms and laboratory tests. Urinary tract infection with a fever of 37 degrees is recommended to go to the hospital, under the guidance of a physician to avoid delaying the condition.