What does a positive nitrite test in urine indicate?

A positive nitrite test in urine indicates the presence of certain types of bacteria, specifically gram-negative bacteria that possess the enzyme nitrate reductase. This enzyme allows these bacteria to convert nitrates, which are normally present in urine, into nitrites, which can then be detected by the nitrite test.

Gram-negative bacteria, such as Escherichia coli, are common pathogens that can cause urinary tract infections (UTIs) and are capable of reducing nitrate to nitrite. Therefore, when a urine sample tests positive for nitrites, it strongly suggests a urinary tract infection caused by one of these gram-negative organisms.

Other options like gram-positive bacteria, urinary crystals, or yeast do not produce nitrites and therefore do not give a positive result on the nitrite test. Gram-positive bacteria typically do not have the necessary enzymes to convert nitrates to nitrites. Additionally, urinary crystals and yeast infections would not result in the production of nitrites either, making them unrelated to the positive nitrite result. Thus, the detection of nitrites is a reliable marker for the presence of gram-negative bacteria in the urine, specifically in the context of diagnosing urinary tract infections.