What does the presence of a large number of white blood cells in urine signify?

The presence of a large number of white blood cells in urine is most commonly associated with infection or inflammation. When the body is responding to an infection, particularly in the urinary tract, white blood cells migrate to the affected area to combat the pathogen. This increase in white blood cells, also known as pyuria, serves as an important indicator to medical professionals of underlying conditions such as urinary tract infections (UTIs), pyelonephritis, or other inflammatory processes affecting the urinary system.

In contrast to other conditions like dehydration, where urine concentration increases without a significant change in white blood cell counts, or kidney stones, which may cause pain and hematuria but not typically an increase in white blood cells, the presence of a high white blood cell count distinctly points towards an infection or inflammatory response. Thus, it is essential for clinicians to recognize this sign in urinalysis as a prompt for further investigation and appropriate management.