Hemosiderin forms due to the breakdown of red blood cells leading to release of hemoglobin which in turn releases iron in your body. Iron deposits in your tissues and produces symptoms. Deposits under the skin cause brownish discolouration. Presence of hemosiderin in urine is called Hemosiderinuria. This is usually seen if you are suffering from excessive breakdown of red blood cells inside the blood vessels as seen in incompatible blood transfusion, severe acute hemolytic anemia or hemochromatosis.