A registered nurse (RN) was a medical degree and a title awarded to a nursing student or practicing nurse upon their completion of a specific level of medical school.
Numerous RNs were reported as WIA, MIA, or KIA by various Federation starships and starbases during the Dominion War. Among those listed on a casualty list in 2374 were: Shirley H. Brand, Ann T. Flood, Teri T. Hansen, Kathy McCammon, Donna W. Nemzek, Nancy B. Ohlson. (DS9: "In the Pale Moonlight")
This designation was only mentioned in writing.