What is blood in urine? Blood in the urine is called hematuria. Blood may color the urine various shades of pink, red and brown. Streaks of blood may also appear in the urine. Visible blood in the urine is called gross hematuria. Blood in the urine may be present in such small quantities that it is not visible by the naked eye, but red blood cells in the urine can be seen with a microscope. This is called microscopic hematuria. The amount of blood in the urine does not always correlate with the seriousness of the disease, disorder or condition. Blood in the urine is often caused by infection, inflammation, or injury of the urinary tract (kidneys, ureters, bladder and urethra). In adults over 35, new-onset hematuria heralds a significant risk of undetected cancer. In some cases, abnormal urine color can be mistaken for blood. In women, blood from the vagina can be mistaken for blood in the urine. In men, prostate problems can lead to blood in the semen, which can also be mistaken for blood in the urine. In addition, certain laxatives and foods can cause the urine to change color. If you can’t attribute the change in color to a medication or something in your diet, abnormal urine color should be evaluated in a medical setting. Blood in the urine can occur in all age groups and populations, and it may or may not occur with additional symptoms.