Hematology is the branch of biology which deals with blood (hemoglobin) and related organs and diseases. Known hematological diseases include hemophilia (TNG: "Loud As A Whisper") and Teplan blight. (DS9: "The Quickening")
Phlox had a degree in hematology. (ENT: "A Night in Sickbay")
Denara Pel was a prominent Vidiian hematologist. (VOY: "Lifesigns")