Two-arm parallel-randomized pilot study and to collect data at the Department of Geriatric Medicine at Aalborg University Hospital. The aim is to assess the feasibility of a future randomized controlled study comparing Danish versions of 3D-CAM and 4AT in an acute medical setting. The primary objective is to assess 1) feasibility of obtaining informed consent and recruiting older adults within 24 hours of admission (or surgery) at the Department of Geriatric Medicine, Department of Acute Medicine, or Department of Orthopedic Surgery. Secondary objectives are 2a) to compare feasibility of recruitment and testing in the three different departments, 2b) to inform a preliminary evaluation of validity and reliability of the Danish version of screening instruments, and 2c) to obtain data on variance to support calculating sample size for a full-scale RCT.

We will recruit participants through a consecutive sampling of all potentially eligible patients. Recruitment will take place in three different settings: the Department of Geriatric Medicine, the Department of Acute Medicine, and the Department of Orthopedic Surgery. One week will be allocated for recruitment in each setting.

Potentially delirious patients often have impaired cognitive status. Therefore, the process of recruitment and informed consent is critically important and poses a central issue of feasibility to be assessed in this study.

It cannot be known with certainty whether patients are delirious prior to inclusion into the study, and even among delirious patients, there are considerable circadian fluctuations (as this is a hallmark of the condition), meaning that patients may have lucid moments during the day where they are cognitively intact and may be able to give informed consent.

Generally, informed consent will be sought from participants when possible. In case they are permanently or temporarily unable to give informed consent, informed consent will be sought from next of kin. Due to the short time in the study for each participant, it is not anticipated that participants will regain the ability to give informed consent during the study. However, if they do, new informed consent will be obtained from the participant. The number of potential participants at each step will be documented to assess problems with feasibility.

Inclusion Criteria:

• Age over 80 years
• Admission or surgery within the last 24 hours

Exclusion Criteria:

• Unable to obtain contact to next of kin for informed consent within time-frame