What is an indicator of bacterial infection in terms of urine composition?

The presence of nitrites in urine is a strong indicator of bacterial infection, particularly urinary tract infections (UTIs). This occurs because certain bacteria that commonly cause UTIs, such as Escherichia coli, have the ability to reduce nitrates, which are normally present in urine, to nitrites. When nitrites are detected during urinalysis, it suggests that these bacteria are present and actively metabolizing the nitrates.

In a healthy individual, nitrites are typically not present in significant amounts because the urinary system usually does not harbor bacteria that can convert nitrates to nitrites. Thus, finding nitrites in a urine sample can prompt further investigation and confirm a suspected infection. This makes it an important marker in the diagnosis of bacterial infections affecting the urinary tract.

High urobilinogen concentrations, presence of ketones, and excess urea may indicate other physiological or metabolic conditions but do not specifically signal bacterial infections in the same manner that nitrite presence does.