In normal people, there is no bacterial growth in the kidney, ureter and bladder; the presence of bacterial growth in these areas, causing an inflammatory response, is called a urinary tract infection. Currently, most specimens are obtained by retaining clean interrupted urine, and urinary tract infections can be diagnosed when their culture counts exceed 100,000 colonies or when two cultures exceed 1,000; specimens obtained by bladder puncture can be diagnosed as urinary tract infections as long as there is colony growth and technical factors are excluded. 1.How many types of urinary tract infections are there? According to the site of infection, urinary tract infections can be divided into pyelonephritis, ureteritis, cystitis and urethritis; according to the duration of the disease, they can be divided into acute and chronic urinary tract infections. However, most units follow the method proposed by Stamm & Hooton in 1993 and classify urinary tract infections into four categories: (1) acute sporadic or recurrent simple cystitis; (2) acute simple pyelonephritis; (3) complicated urinary tract infections; and (4) asymptomatic bacteriuria. 2.What tests are useful for the diagnosis of urinary tract infection? In addition to bacterial culture, test paper, microscopy, immunofluorescence, excretory function assay and imaging are commonly used. The test paper method detects urine nitrogenous compounds, which must be morning urine to be valuable; leukocyte lipoproteinase is more sensitive and is missed in about 25% of patients. Urine microscopy reveals bacteria, pus cells and red blood cells should be highly suspicious of urinary tract infection, and leukocyte tubularity has diagnostic value for pyelonephritis. Urinary function tests for urethral sphincter function are of great value for vesicoureteral reflux, neurogenic bladder, and peripheral neuropathy in diabetes mellitus. Among imaging tests, abdominal plain films are the most valuable, while CT, MRI, and nuclear scans are only effective in determining susceptibility factors. Antibody-encapsulated bacteria, urine enzyme assay, urine β2-microglobulin assay, urine osmolality assay, Tamm-Horsfall protein and its antibody assay, and serum antibodies against Gram-negative bacterial “O” antigen assay are helpful in localizing the diagnosis. 3.What are the common clinical manifestations of pyelonephritis? What are the serious complications? In addition to the general symptoms of urinary tract infection, such as frequent urination, urgent urination and cloudy urine, typical pyelonephritis also presents with back pain, chills, fever and lumbar tenderness, and some patients may experience nausea, vomiting and dehydration. Its more serious complications include renal papillary necrosis, perirenal abscess, Gram-negative bacterial sepsis, yellow granulomatous pyelonephritis, acute renal failure, unifocal or multifocal bacterial acute interstitial nephritis and renal scarring.