- Pyuria, defined as the presence of leukocytes or pus cells in the urine, is a key indicator of an inflammatory response in the urinary tract and strongly suggests infection.
- While bacteriuria may be present in contamination or asymptomatic bacteriuria, and hematuria or proteinuria can occur in various renal pathologies, pyuria specifically reflects active infection due to immune response against invading pathogens.
- Thus, pyuria is diagnostic of urinary tract infection (UTI), as it demonstrates evidence of inflammation and immune activity within the urinary tract.

Reference: Davidson’s Principles and Practice of Medicine, 23rd Edition, Chapter: The urinary tract, Page 593.