Urine, blood in

[Michiko]

Blood in the urine (hematuria) can make urine appear pink, red, or brown, depending on the amount of blood, how long it has been in the urine, and how acidic the urine is. An amount of blood too small to change color of the urine (microscopic hematuria) may be found by chemical tests or microscopic examination. Microscopic hematuria may be found when a urine test is done for another reason.
People with hematuria may have other symptoms of urinary tract disorders, such as pain in the side or back (flank), lower abdominal pain, an urgent need to urinate, or difficulty urinating, depending on the cause of blood in the urine. If sufficient blood is present in the urine, the blood may form a clot. The clot can completely block the flow of urine, causing sudden extreme pain and inability to urinate. Bleeding severe enough to cause such a clot is usually caused by an injury to the urinary tract.
Red urine is not always caused by red blood cells. Red or reddish brown discoloration may also result from the following:

Hemoglobin (which carries oxygen in red blood cells) in the urine due to the breakdown of red blood cells
Muscle protein (myoglobin) in urine due to the breakdown of muscle cells
Porphyria (a disorder caused by deficiencies of enzymes involved in the production of heme, a chemical compound that contains iron and gives blood its red color)
Foods (for example, beets, rhubarb, and sometimes food coloring)
Drugs (most commonly phenazopyridine , but sometimes cascara, diphenylhydantoin, methyldopa , rifampin , phenacetin, phenothiazines, and senna)