Urinary tract infections are the most common abnormality detected in a urine test. These infections are characterized by the presence of numerous leukocytes (positive leukocyte esterase test) and bacteria (often with a positive nitrite test). However, bacteria can also be seen when the specimen is contaminated during urine collection. In cases of contamination, the bacteria will be accompanied by a small number of leukocytes. The presence of numerous squamous cells (see if this observation is noted) suggests that the bacteria could have come from external genital tracts. However, a positive nitrite test points strongly to a urinary tract infection.