WBC are reported semiquantitatively as the number seen per high power field (HPF) using the high dry objective (40x):
Interpretation: Less than 5 WBC/HPF is 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.
Identification: In regular unstained urine sediments, WBC are small cells, usually 1.5-2x larger than a RBC (see image below), are regularly round, colorless and have a slightly grainy appearance. Like erythrocytes, WBC may lyse in very dilute or highly alkaline urine. The type of WBC (neutrophil, lymphocyte, monocyte etc) cannot be determined from a regular urine wet preparation, but they are usually neutrophils. A cytologic examination would be required to determine which WBC types are present in urine, however this is rarely indicated for this purpose.
WBC must be distinguished from RBCs and small epithelial cells.
For a compilation of images of the different cells seen in urine, see the urine
© Cornell University