Incidence and range of microscopic hematuria in patients with indwelling urinary catheters.

The presence and number of red blood cells (RBCs) in the urine after catheterization were ascertained in 40 patients without urinary tract pathology or other cause for hematuria. Before catheterization, 90% of the patients had less than or equal to 1 RBC/high power field (HPF), a figure similar to that for normal volunteers. Two days after catheterization, however, 61,5% of the patients had 2 RBC/HPF with a range between zero and "too numerous to count." The incidence of "hematuria" (greater than or equal to 2 RBC/HPF) declined with time. Neither urinary specific gravity nor urinary tract infection could be correlated with hematuria. At any time after catheterization, 90% of the patients had greater than or equal to 50 RBC/HPF. These data may be helpful in differentiating hematuria caused by the catheter from that due to drug reactions or disease states.