One point each is given for the numbers 1, 2, 4, 5, 7, 8, 10, and 11 if at least half the area of the number is in the proper octant of the circle relative to the number 12. One point each is given for an obvious short hand pointing at the 11 and an obvious long hand pointing to the 2. The difference in the length of the hands must be obvious at a glance. The advantage of a large (relative to the size of handwritten numbers), uniform, standard-sized circle is that it permits scoring based on the position of the numbers (Figure 1).
Interpretation of the Score for Cognitive Impairment
A score of 10 suggests that cognitive impairment (CI) is unlikely, although isolated short-term memory impairment such as that seen with carbon monoxide poisoning may be missed. A score of eight or nine must be interpreted clinically. However, a score of less than eight indicates almost CI, and a score of less than five indicates prominent impairment. In medically stable patients, scores remain stable from one day to the next. Interrater reliability is good and the clock scores correlate with a number of formal neuropsychological tests.
Two gerontologists administered the 10-point clock test to a series of ambulatory outpatients with dementia (mean Mini-Mental State Examination [MMSE] score=20)-principally Alzheimer's disease but also multi-infarct dementia and mixed or atypical dementia (Folstein et al., 1975). Seventy-six percent scored less than eight points. These data were reanalyzed (Manos, in press) for 16 patients with Alzheimer's disease and MMSE scores greater than 23 (mean score = 26). Seventy percent of these very mildly impaired patients scored less than eight points. Eighty-two percent of control subjects (mean age 78) scored greater than seven points.
Hence, this quick screen can be helpful in the office with patients whose difficulty may escape casual questioning.
Test Utility in the General Hospital
When nurses rated their medical and surgical inpatients on a clinical scale of CI (0=none, 4=severe), the Spearman's correlation between clock scores and nursing scores was 0.6, i.e., the more impaired the patients, the lower the clock score. In a separate study of patients referred for psychiatric consultation (Manos, 1997), the test was particularly sensitive to dementia and delirium, but also identified a significant fraction of patients with opioid intoxication, and the less well-defined DSM-IV diagnosis of cognitive disorder not otherwise specified.
For the diagnosis adjustment reaction, in which minimal cognitive disturbance is expected, only 5% of patients scored less than eight points (Table).
Note that none of the patients with major depression, alcohol(Drug information on alcohol) dependence and adjustment reaction scored less than five points. This observation is the basis for "prominent" designation of the CI identified by a score of less than five. Note also that none of the patients with dementia or delirium scored 10 points, and only 10% and 14% of patients with opioid intoxication or cognitive disorder not otherwise specified, respectively, did so. This is the basis for saying that a score of 10 suggests CI is unlikely.
Any of the 11 medical problems listed in the first paragraph can disturb any test of cognition; hence, without a medical history, no cognitive test makes a diagnosis. A score of less than eight on the 10-point clock test indicates CI. It does not replace formal testing in the domains of memory, for example, or word fluency. It is not an alternative to formal neuropsychiatric testing when that is clinically indicated. The clinician, not the clock test score, determines what is to be done next.