Sterile Pyuria

Pyuria is defined as the presence of 10 or more white cells per cubic millimeter in a urine specimen, 3 or more white cells per high-power field of unspun urine, a positive result on Gram's staining of an unspun urine specimen, or a urinary dipstick test that is positive for leukocyte esterase.(1) Sterile pyuria is the persistent finding of white cells in the urine in the absence of bacteria, as determined by means of aerobic laboratory techniques (on a 5% sheep-blood agar plate and MacConkey agar plate). Sterile pyuria is a highly prevalent condition, and population-based studies show that 13.9% of women and 2.6% of men are affected.(2) Specific populations have a higher risk of this condition; for example, the frequency of detection of sterile pyuria was 23% among inpatients in one study (excluding those with urinary tract infection), and sterile pyuria is more common among women than among men because of pelvic infection.(3) Subsequent to initial detection, the costs of laboratory, radiographic, and invasive evaluation in such large populations can have a considerable effect on health care expenditures.(4) Although colony counts greater than 100,000 colony-forming units (CFU) per milliliter in voided urine have historically been used to distinguish bacterial urinary tract infection from colonization,(5) many U. S. laboratories currently report bacterial colony counts of more than 1000 CFU per milliliter in urine as being diagnostic of bacteriuria.(6) It is important to consider that lower bacterial counts can be associated with urinary tract infection. Contemporary studies indicate that a colony count of 100,000 CFU per milliliter would differentiate clinically significant from clinically nonsignificant infections and thus reduce the number of positive cultures by 38% relative to the number of cultures that would be considered positive with the 1000 CFU per milliliter cutoff point. Use of the higher cutoff point as the level to treat could also decrease the use of antibiotics.(6) In this article, we review causes of sterile pyuria and describe a clinical approach to its evaluation.