Hemoglobin

Hemoglobin was the compound in red blood cells that gave them their red color and served to convey oxygen to the body tissues. Human hemoglobin was iron-based, while Vulcan hemoglobin was copper-based and green in color. ; ;

In 2268, after Leonard McCoy had received treatment for his xenopolycythemia, Spock reported that the doctor's hemoglobin count was back to normal. 

Terran leeches consumed hemoglobin.