Final answer:
A urinalysis finding that indicates a urinary tract infection is the presence of leukocyte esterase, which is released by white blood cells and serves as an indirect indicator of infection.
Step-by-step explanation:
Leukoesterase is an enzyme produced by leukocytes, also known as white blood cells, which can be detected in urine. When urinary tract infections occur, the number of leukocytes in the urine increases as they are mobilized to fight the infection. Leukoesterase is released by these leukocytes, and its presence in the urine serves as indirect evidence of an infection. Unlike other substances such as crystals, bilirubin, and ketones which can be present due to various reasons not specific to UTIs, the detection of leukoesterase is particularly indicative of an active urinary tract infection.
Furthermore, routine manual urinalysis using a urine dipstick can swiftly screen for signs of infection such as nitrites and leukocyte esterase. If either of these is present, especially leukocyte esterase, it often prompts further testing, such as a urine culture, to confirm the presence of a bacterial infection and to determine the causative organism.