False Positive and Negative Urine Leukocyte Esterase
A false positive result may occur in the presence of strong oxidizing agents in the collection container. In random urine specimens from women, a positive result for leukocyte esterase may be due to a source external to the urinary tract.
Other urine sediment findings such as bacteria, squamous or renal epithelial cells, lymphocytes or red blood cells do not contain esterases, and would not produce a positive leukocyte esterase test.
False negative results may occur in the presence of significant levels of protein or glucose and in urines with high specific gravity which can crenate the white blood cells, leaving them unable to release esterases. Some drugs such as Cephalexin (Kelfex®), Cephalothin Keflin®), Tetracycline, or high concentrations of oxalic acid may also cause falsely decrease leukocyte esterase test results.