The presence of red and white blood cells together in the urine often indicates inflammation or bacterial infection of the kidney or urinary tract, notes WebMD. Leukocytes, or white blood cells, in significant numbers generally signal infection, while red blood cells in sufficient quantity indicate disease or trauma of the organs of the urinary system, states the Johns Hopkins Lupus Center. However, it is possible for red or white blood cells to occur in a urine sample for other reasons.
Even small increases in the incidence of red blood cells in a urine sample warrant attention, but blood from hemorrhoids or menstruation sometimes contaminates a sample and skews the result of urinalysis, explains the American Association for Clinical Chemistry. Other causes of red blood cells in urine that potentially signal health problems include smoking, the use of some medications and strenuous exercise, reports the Johns Hopkins Lupus Center.
White blood cells also sometimes show up during urinalysis due to sample contamination, but their presence otherwise typically indicates infection, according to the Johns Hopkins Lupus Center. While bacteria is the most common culprit, the incidence of white blood cells in a urine sample with an absence of bacteria indicates a condition called urethral syndrome, says WebMD. Thirty to 50 percent of people who experience the symptoms of a urinary tract infection have this condition. Potential causes include many of the same organisms that cause vaginal infections: chlamydia, gonorrhea, trichomoniads and Ureaplasma urealyticum.