What is the key indicator of a urinary tract infection in urine analysis?

The presence of nitrites in a urine analysis is a key indicator of a urinary tract infection (UTI) because certain types of bacteria that commonly cause UTIs, such as Escherichia coli, convert nitrates, which are normally found in urine, into nitrites. This conversion occurs when the urine is in contact with the bacteria which thrive in the urinary tract. Thus, detecting nitrites in the urine serves as a useful screening tool for the presence of an ongoing infection.

In addition to nitrites, other analyses such as the presence of white blood cells or bacteria may support a diagnosis of UTI, but nitrites are specifically indicative of bacterial activity associated with infection. The other options provided do not have the same direct link to urinary tract infections. High glucose levels could suggest diabetes, low protein levels generally indicate normal kidney function, and high bilirubin levels might pertain to liver dysfunction rather than urinary tract infections. Consequently, the presence of nitrites is a focused and specific marker for diagnosing UTIs in urine analysis.