Assessing severity of delirium by the Delirium Observation Screening Scale Alice C. Scheffer 1 , Barbara C. van Munster 1 , Marieke J. Schuurmans 2 and Sophia E. de Rooij 1 1 Department of Internal and Geriatric Medicine, Academic Medical Center, Amsterdam, The Netherlands 2 Department of Health Science, University Medical Center, Utrecht, The Netherlands Correspondence to: A. C. Scheffer, RN, MSc, E-mail: a.c.scheffer@amc.uva.nl Objective: Delirium is the most common acute neuropsychiatric disorder in hospitalized elderly. Assessment of the severity of delirium is important for adjusting medication. The minimal dose of medication is preferable to prevent side effects. Only few nurse based severity measures are available. The aim of this study was to validate a scale developed to assess symptoms of delirium during regular nursing care, the Delirium Observation Screening (DOS) Scale, for monitoring severity of delirium. Method: Delirious patients of 65 years and older were included. Delirium was diagnosed according to DSM-IV criteria and the Confusion Assessment Method. The DOS Scale was compared to the Dutch version of the Delirium Rating Scale-Revised-98 (DRS-R-98). Global cognitive functioning was assessed by the Informant Questionnaire Cognitive Decline in the Elderly-Short Form (IQCODE-SF) and the KATZ-ADL Scale was used for functional impairment. Results: Ninety seven delirious patients were included: 41 hip fracture patients and 56 medical patients. The correlation between total DRS-R-98 scores and DOS Scale scores was 0.67 ( p ¼ 0.01). For the cognitive impaired group (IQCODE-SF 3.9) this correlation was 0.61 ( p ¼ 0.01); for the group with no global cognitive impairment, this correlation was 0.67 ( p ¼ 0.01). Correlations between DRS-R-98 and DOS Scale for hypoactive, hyperactive and mixed delirium subtype were 0.40 ( p ¼ 0.32), 0.44 ( p ¼ 0.01) and 0.69 ( p ¼ 0.05), respectively. Conclusions: The DOS Scale is able to measure severity of delirium. In routine daily clinical practice, the DOS Scale is a time-efficient, easy to use and reliable method for measuring and monitoring severity of delirium by nurses. Copyright # 2010 John Wiley & Sons, Ltd. Key words: delirium; severity; DRS-R-98; DOS Scale History: Received 24 November 2009; Accepted 8 March 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/gps.2526 Introduction Delirium is an acute neuropsychiatric syndrome with a typical fluctuating course, deranged consciousness and cognitive and attentional disturbances. Delirium is common in hospitalized older patients and is associated with many serious short- and long-term consequences including increased length of hospital stay, increased morbidity and hospital mortality and higher hospital costs (Williams et al., 1988; Francis et al., 1990; O’Keeffe and Lavan, 1997; Dolan et al., 2000; Ely et al., 2001; McCusker et al., 2003). After diagnosing deliriumm, it is important to closely observe the severity of delirium for adaptation of medication as this medication may cause unfavourable side effects. In order to assess severity of delirium, many different instruments have been developed both for clinical and research use. Frequently used scales for assessment of the severity of delirium are the Delirium Detection Score (Otter et al., 2005) for severity of delirium in the ICU, the MDAS (Williams et al., 1988; Breitbart et al., 1997) or the Delirium Rating Scale (DRS) (Trzepacz et al., 1988). The most widely used instrument to diagnose delirium and to assess severity is RESEARCH ARTICLE Copyright # 2010 John Wiley & Sons, Ltd. Int J Geriatr Psychiatry (2010)