Hematin is a dark brown or black crystalline compound derived from the breakdown of hemoglobin, the protein in red blood cells that carries oxygen. It is formed when heme, the iron-containing component of hemoglobin, is oxidized. Hematin is often used in laboratory settings for various biochemical applications, including studies related to blood and oxygen transport. In medicine, hematin can be used to treat certain conditions, such as acute intermittent porphyria, a disorder that affects heme production. It helps to alleviate symptoms by providing a source of heme, which can reduce the buildup of toxic substances in the body.