A 56-year-old man presents for evaluation. He has a family history as well as personal history of alcohol use disorder but his recent drinking status is unclear. He has no history of a psychotic, mood, or anxiety disorder. He does not smoke and he denies use of illicit drugs. Of the following, which is the most helpful to assess abstinence in someone with alcohol use disorder? Alanine aminotransferase Aspartate transaminase Carbohydrate deficient transferrin Mean corpuscular volume