A 79-year-old woman is admitted for pneumonia. On day 3 of hospitalization, she becomes disoriented to place, demonstrates fluctuating levels of alertness, and shows difficulty sustaining attention. Her daughter states that although her mother has mild memory problems at home, she has never experienced this type of confusion. The nurse suspects delirium, but notes the presence of pre-existing mild Cognitive impairment. Which screening tool should the nurse prioritize to most accurately identify acute delirium in this client?

A. Mini-Mental State Examination (MMSE): MMSE measures global cognition and can track chronic deficits but is not designed to detect the acute onset and fluctuating course of delirium. B. Geriatric Depression Scale (GDS): GDS screens for depression; mood disorders may mimic cognitive change but the GDS does not identify the acute inattention and fluctuating consciousness characteristic of delirium. C. Montreal Cognitive Assessment (MoCA): MoCA detects mild cognitive impairment and subtle chronic cognitive deficits but is not a delirium-specific screening instrument. D. Confusion Assessment Method (CAM): CAM is a validated bedside tool specifically designed to identify delirium (acute onset, fluctuating course, inattention, disorganized thinking or altered level of consciousness) and is the preferred choice to distinguish acute delirium from baseline cognitive impairment.