Blood in your urine can indicate a problem with your kidneys or another component of your urinary tract. The medical term for blood in your pee is hematuria. Hematuria is classified into two types: Gross hematuria occurs when there is visible blood in the urine. Microscopic hematuria refers to the presence of red blood cells on the microscope slide but not enough to see from outside the body. Having microscopic amounts of blood in your urine can be a sign of many health problems, including kidney disease, malignancies, and infections. Gross hematuria can be caused by many different conditions, most often involving the kidneys. These include diseases such as glomerulonephritis (an inflammatory disease that affects the structure of the kidney filtration system) and vasculitis (when blood vessels become inflamed). Other possible causes include trauma to the bladder or upper part of the urethra, radiation therapy to the pelvic area, and certain metabolic disorders such as porphyria (when blood cells are destroyed before they can disintegrate). Some factors such as fever, infection, or physical activity may cause blood to appear in your urine. So too might medications such as acetylsalicylic acid (aspirin), NSAIDs (non-steroidal anti-inflammatory drugs), or alcohol. These substances can also cause bleeding into the urine stream. Sexual activity can also lead to blood in the urine.