What Does Esterase in Urine Mean?

A positive leukocyte esterase test indicates the individual may have a urinary tract infection, according to MedlinePlus. In order to confirm the infection, the lab examines the urine under a microscope to detect the presence of white blood cells. The test involves normal urination and causes no discomfort.

Receiving a negative leukocyte esterase is normal, making it unlikely the patient has a urinary infection; however, high levels of protein or vitamin C in the urine sometimes cause a false negative result. False positive test results sometimes result from other types of infections or vaginal secretions in women, reports MedlinePlus.

Luekocyte esterase is an enzyme found in the white blood cells. Doctors use its presence in urine as an indicator of white blood cells. The presence of such cells is usually an indicator of bacterial infections. However, contamination of the sample also increases the white blood cells in urine, so patients should use the cleaning supplies provided with the urine collection kit to provide an aseptic sample, according to Johns Hopkins Lupus Center.

After collecting the sample, the health care provider places a dipstick into the sample. The pad on the dipstick changes colors in the presence of leukocyte esterase for a positive test, according to MedlinePlus.