Urine Dipstick: Urinary Nitrites and Leukocyte Esterase - Dipping into Murky Waters

Abstract

The urine dipstick is used in combination with other clinical and microbiologic data to diagnose urinary tract infections (UTIs). It is usually ‘first-line’ in diagnosis given the ease of testing, low cost, and ability to use as a point-of-care test. Two components of the dipstick that are utilized in assisting in the diagnosis of UTIs are leukocyte esterase and nitrites. Leukocyte esterase is an enzyme that is released by white blood cells (WBCs) and therefore correlates with pyuria. Some bacteria (such as E. coli) convert urinary nitrates that are routinely present in the urine into nitrite. Therefore, a positive nitrite test on the urine dipstick is suggestive of the presence of these organisms. Importantly, a positive dipstick result only suggests the presence of bacteriuria and does not help in distinguishing between asymptomatic bacteriuria and symptomatic UTI. False positive and false negative dipstick tests are also common, and consideration should be given to the clinical context when interpreting results. When considering the diagnosis of a urinary tract infection, the dipstick result should therefore be used with careful interpretation of symptoms, urine microscopy, and urine culture along with consideration of other potentially confounding diagnoses such as sexually transmitted infections (STI) and vaginosis.