Normal leukocyte esterase levels are negative, according to MedlinePlus. Negative results indicate the absence of white blood cells in urine and that the patient does not have an infection.
The leukocyte esterase test is done using a color-sensitive dipstick that changes color to indicate the presence of white blood cells in urine, explains MedlinePlus. Normal ranges may vary among different laboratories, and vaginal secretions or high levels of protein or vitamin C may interfere with the test results to create false positives or false negatives. If the levels of white blood cells indicate a positive result, the urine typically goes through a microscopic exam in order to check for the specific infection.