Urine Nitrite

This part of a urine dipstick test checks for nitrite. Your urine normally contains nitrate from your diet, and certain bacteria convert that nitrate into nitrite. So while dietary nitrate itself is normal, nitrite is not, and a positive result points to bacteria in the urinary tract.

Because the bacteria need time to convert nitrate into nitrite, the test works best on urine that has stayed in the bladder for several hours, such as a first morning sample. A positive nitrite is a strong hint of a urinary tract infection, especially together with leukocytes.

A negative nitrite does not rule out infection: some bacteria do not convert nitrate at all, and a very dilute or fresh sample can read negative despite bacteria being present.

Nitrite is valuable because it is fairly specific: when it is positive, bacteria that convert nitrate are almost always present. That makes it a quick, low-cost pointer toward a bacterial urinary tract infection before a culture is available.

The flip side is its low sensitivity. Common bacteria such as certain streptococci and staphylococci do not produce nitrite, so the test misses them. This is why nitrite is never read on its own but always alongside leukocytes, symptoms and, when needed, a urine culture.

Together, a positive nitrite and positive leukocytes make a urinary tract infection much more likely than either result alone.

Nitrite is checked whenever a urinary tract infection is suspected, for instance with painful or frequent urination, cloudy urine, or lower abdominal pain. It is a standard part of the dipstick during many general check-ups as well.

For a reliable result, a clean-catch sample from urine that has been in the bladder for a few hours works best. If symptoms persist while the dipstick stays negative, your doctor may still request a urine culture, because a negative nitrite does not exclude an infection.