Delirium is a common neuropsychiatric syndrome associated with serious adverse healthcare outcomes. It is misdiagnosed in over 50% of cases across healthcare settings.

To document the point prevalence of delirium across an acute general hospital and identify factors associated with accurate detection by medical and nursing staff, as well as patient and carer recognition.

Adult in-patients in Cork University Hospital on 15.05.2010 were assessed for inattention, delirium symptoms with the Revised Delirium Rating Scale (DRS-R98) and the Confusion Assessment Method (CAM), and pre-existing cognitive impairment with the Informant Questionnaire for Cognitive Decline (IQCODE). Recognition by patients/carers and nursing staff was assessed through direct questioning, while recognition by the treating medical team was assessed through casenote review.

311 were recruited (87% of inpatients). 55(18%) had delirium. Pre-existing cognitive decline was detected in 28 delirious patients(51%). of those with delirium, 17 (31%) were aware of their own confusion, 35(64%) were recognised by nursing staff, and 24 (44%) had delirium documented in medical casenotes. Predictors of recognition in medical casenotes were the severity of inattention, short-term memory impairment and being managed by a medical rather than surgical team. for nurse recognition, predictors were severity of delusions, affective lability, inattention and long-term memory impairment. for patient self-recognition, acuity of onset and disorientation were predictors.

Delirium is present in approximately one in five hospitalised inpatients at any time. Under-detection is common. Factors linked to accurate detection can inform educational and other efforts to improve delirium recognition.

The frequency of full syndromal and subsyndromal delirium is understudied.

We conducted a point prevalence study in a general hospital.

Possible delirium identified by testing for inattention was evaluated regarding delirium status (full/subsyndromal delirium) using categorical (Confusion Assessment Method (CAM), DSM-IV) and dimensional (Delirium Rating Scale-Revised-98 (DRS-R98) scores) methods.

In total 162 of 311 patients (52%) screened positive for inattention. Delirium was diagnosed in 55 patients (17.7%) using DSM-IV, 52 (16.7%) using CAM and 58 (18.6%) using DRS-R98⩾12 with concordance for 38 (12.2%) individuals. Subsyndromal delirium was identified in 24 patients (7.7%) using a DRS-R98 score of 7–11 and 41 (13.2%) using 2/4 CAM criteria. Subsyndromal delirium with inattention (v. without) had greater disturbance of multiple delirium symptoms.

The point prevalence of delirium and subsyndromal delirium was 25%. There was modest concordance between DRS-R98, DSM-IV and CAM delirium diagnoses. Inattention should be central to subsyndromal delirium definitions.