Home / papers / Sample Essay:The Reliability and validity of the confusion assessment method (CAM).

Sample Essay:The Reliability and validity of the confusion assessment method (CAM).

I am a registered nurse working in a general medical ward. We have many elderly patients with a range of disease processes. Our patients may also present with existing cognitive dysfunction and/or temporary altered mental states including delirium. These altered mental states may be the result of underlying physiological alterations such as urinary tract infections or cardiac arrhythmias and transient ischaemic attacks, may result as a side effect of drug therapies or may exacerbate confusion in older people with mild cognitive dysfunction following a change in physical environment (Alagiakrishnan, 2015). (Introduction of my role as RN in ICU …)

(population of Traumatic brain injury in intensive care unit).

Delirium is a common and serious problem affecting older adults, associated with increased mortality, prolonged hospital stays, increased healthcare costs, higher rates of institutionalisation, and decreased functional independence (Adamis et al, 2006). Delirium increases hospital costs by at least $2,500 per patient, resulting in over $6.9 billion (2004 USD) in hospital costs each year (Inouye 2006). Despite its adverse impact, delirium remains poorly recognised in clinical practice. The Confusion Assessment Method is a delirium instrument, first published in 1990 (Inouye, et al) which was created to improve the identification of delirium. Because of its accuracy, brevity, and ease of use by clinical and lay interviewers, the CAM has become the most widely used standardised delirium instrument for clinical and research purposes (Wei, et al 2008).

Traumatic Brain Injury AND GCS tool.

The CAM was designed to allow non-psychiatric clinicians to diagnose delirium quickly and accurately following brief formal cognitive testing. The CAM instrument assesses the presence, severity, and fluctuation of 9 delirium features: acute onset, inattention, disorganised thinking, altered level of consciousness, disorientation, memory impairment, perceptual disturbances, psychomotor agitation or retardation, and altered sleep-wake cycle. The CAM diagnostic algorithm is based on four cardinal features of delirium: 1) acute onset and fluctuating course, 2) inattention, 3) disorganised thinking, and 4) altered level of consciousness. A diagnosis of delirium, according to the CAM, requires the presence of features 1, 2, and either 3 or 4 (Wei, et al 2008).

Tool Definition

Originally developed by literature review and expert consensus, the CAM was validated for content validity against the reference standard ratings of geropsychiatrists, based on the Diagnostic and Statistical Manual for Mental Disorders Third Edition Revised (DSM-IIIR) American Psychiatric Association (1987) criteria. Content validity requires the use of recognised experts in the field to evaluate whether test items actually assess what the tool means to assess (Nestle Nutrition Institute, ND). Several studies included expert assessments (geriatrician, psychiatrist, neuropsychologists and advanced practice nurses) applying DSM-III, DSM-IIIR, DSM-IV, or ICD-10 criteria or a consensus diagnosis (Inouye, et al 1990; Ely, Inouye, et al 2001; Ely, Margolin, et al 2001; Fabbri et al, 2001; Gonzalez, 2004; Laurila, et al 2002; Monette, et al 2002; Pompei, et al, 1995;  Rockwood, et al 1994; Rolfson, et al 1999; Zou, et al 1998).


The sensitivity of the CAM ranges in high quality studies (Inouye, et al 1990; Ely, Inouye, et al 2001; Ely, Margolin, et al 2001; Fabbri et al, 2001; Gonzalez, et al 2004; Laurila, et al 2002; Monette, et al 2002; Zou, et al 1998) from 94-100%, meaning that it has a strong likelihood that it will detect delirium when it is used in the context for which it was designed (Nestle Nutrition Institute, ND). Some lower quality studies yielded poorer sensitivity results (40 – 70%) and this was attributed to reasons such as nurses or research assistants conducting the ratings with extremely brief cognitive assessments (e.g., attention tasks alone)(Rockwood, et al 1994), without formal training in the use of the CAM (Pompei, et al 1995; Rockwood, et al 1994), or in populations with high rates of dementia (Rockwood, et al 1994).  


The CAM demonstrated specificities from 89–95% (Inouye, et al 1990; Ely, Inouye, et al 2001; Ely, Margolin, et al 2001; Fabbri, et al, 2001; Gonzalez, et al 2004; Monette, et al 2002; Pompei, et al 1995;  Rockwood, et al 1994; Rolfson, et al 1999; Zou, et al 1998), again, when it was used in the correct context (Wei, et al 2008). This means it is likely to give negative results in those who do not have delirium (Nestle Nutrition Institute, ND). When used in an inappropriate sample that included a large proportion of patients with dementia (43%), depression (15%) and psychosis (4%), a low specificity (63%) was detected, probably confounding delirium recognition (Laurila, et al 2002). The accuracy of the CAM rating is improved when formal cognitive testing is used prior to the rating with a tool such as the Mini Mental State Exam (MMSE) (Inouye, et al 1990, Inouye, Foreman, et al 2001).

Building on these concepts, the CAM had a positive predictive accuracy of 91– 94% (ie. how many of the subjects who tested positive truly have delirium (Nestle Nutrition Institute, ND), and a negative predictive accuracy of 90–100%, (ie How many of the subjects who test negative truly do not have delirium (Nestle Nutrition Institute, ND).

Several studies explored interrater reliability of the CAM. This determines that results obtained by different investigators are consistent when repeated in the same subjects (Nestle Nutrition Institute, ND). Interrater reliability in high quality studies ranged from .81–1.00 (the closer the value is to 1.0, the more reliable the tool is between raters) (Nestle Nutrition Institute, ND). Studies that compared nurse to physician rating of the CAM found that physician-rated scores had higher sensitivities (Rockwood, et al 1994; Rolfson, et al 1999). Appropriate training of the interviewers is crucial for accurate CAM ratings (Wei, et al 2008).


Adaptations of the CAM have been developed to address specific patient populations, such as the CAM-ICU for non-verbal, ventilated patients and adapted versions for the emergency department and nursing home populations (Wei, et al 2008). adaption

Based on a systematic review of the CAM, several recommendations are proposed to optimise the use of the instrument for the identification of delirium in the context of my medical ward. Some training is recommended for optimal use. The Confusion Assessment Method Training Manual is available online to facilitate this process (Inouye 2003). Moreover, the CAM was designed to be scored based on observations made during formal cognitive assessment, such as with brief instruments like the MMSE or Short Portable Mental Status Questionnaire (SPMSQ). Without such formal assessment (or with extremely brief assessments), the sensitivity of the CAM for delirium detection is compromised. For research purposes, use of the full 9-item CAM instrument is recommended to maximise sensitivity for the detection of delirium (Wei, et al 2008).

Many of these studies are older, being performed around the early 2000’s. There may be some historical factors that may have changed over the last 15 years, for example clinician familiarity with this now widely used tool could influence these results if they were replicated now.

An important caveat about use of the CAM is worthy of comment. Given its imperfect sensitivity, it is not recommended as the sole means for identification of delirium in the clinical setting. The use of astute clinical judgment combined with other formal cognitive screening measures is required to avoid missing hypoactive, subtle, or atypical cases of delirium (Wei, et al 2008).