Quantitative Urinalysis

Using a hemocytometer, we determined the number of white blood cells (WBCs) per milliliter in uncentrifuged urine specimens. Uninfected urine usually contained ≤ 10³WBCs per milliliter, although up to 8×10³WBCs per milliliter were observed. Infected urine regularly contained >10⁴WBCs per milliliter, and the mean WBC count per millimeter for urine from infected patients was 3.1×10⁵. The absence of pyuria thus provides strong evidence against the presence of urinary tract infection. Similar results were obtained in patients who had indwelling catheters, suggesting that bacteriuria reflects the presence of infection rather than colonization. Valid data are easily obtainable by quantitative urinalysis of uncentrifuged urine specimens. There are obvious differences in WBCs per milliliter, with little overlap between infected and uninfected urine. This method of analysis should replace traditional means of counting WBCs per visual field in a centrifuged, resuspended urine sediment. (JAMA236:2069-2072, 1976)