The presence of leukocytes (white blood cells) in urine sediment usually confirms a positive leukocyte (esterase) result. Since the leukocyte esterase test detects intact or broken leukocytes, it might not be possible to confirm the test under a microscope when overly diluted urine causes the leukocytes to burst. Leukocytes are abundant in vaginal secretions, and specimen contamination is frequent.
If not due to contamination, the repeated presence, in urine, of 3 to 5 leukocytes per field suggests a low urinary tract (bladder and urethra) infection. In the presence of bacteria or a positive nitrite test in a symptomatic patient, the presence of leukocytes confirms a urinary tract infection. In the absence of bacteria, the presence of leukocytes may instead indicate an inflammatory process (interstitial nephritis, cystitis, etc.), a kidney stone, a tumour of the bladder or urethra, or the presence of an atypical infection (chlamydia, ureaplasma, tuberculosis).
Pus is an accumulation of white blood cells. The observation of pus in urinary sediments simply means that the number of leukocytes was very high. The presence of pus can sometimes prevent other elements present in the specimen from being detected under a microscope.