甲 is the first of the ten Heavenly Stems, used for "first" or "grade A". The palace examination sorted its graduates into three classes, and
一甲 held only the top three:
状元,
榜眼 and
探花. Hospitals are graded by level and then A, B or C, so
一甲 (level one, grade A) is a small local hospital and
三甲 the top rating.
一 keeps its first tone here because it means "first".
