In a urine test, the detection of red blood cells (erythrocytes) above a certain threshold may indicate the presence of bleeding in the urinary tract. In a blood test, red blood cell counts falling outside the established reference ranges for age and gender may point to a potential health issue. These reference ranges are generally as follows: For adult males, 4.7–6.1 million cells/microliter; for adult females, 4.2–5.4 million cells/microliter; for newborns, 4.8–7.2 million cells/microliter; and for children, 4.6–4.8 million cells/microliter.