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Abstract
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 non-significant 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. In this article, we review causes of sterile pyuria and describe a clinical approach to its evaluation.