White blood cells (WBC) in unstained urine sediments typically appear as round, granular
cells which are1.5-2.0 times the diameter of RBC. The details of nuclear shape often are
difficult to discern, especially if the specimen is not fresh. WBC in urine are most commonly
neutrophils. Staining of air-dried sediment smears with a hematologic stain sometimes is
useful for more specific identification. Like erythrocytes, WBC may lyse in very dilute or highly
alkaline urine.
WBC up to 5/HPF are commonly accepted as normal. Greater numbers (pyuria) generally indicate the presence of an inflammatory process somewhere along the course of the urinary tract (or urogenital tract in voided specimens). Pyuria often is caused by urinary tract infection, and many times bacteria can be seen on sediment preps. Depending on clinical signs, pyuria may be an indication for culture of urine even if no bacteria are seen. Non-septic causes of inflammation, such as uroliths and tumors, also must be considered. |
Last Updated: January 16, 1996