The utility of the clock drawing test in detection of delirium in elderly hospitalised patients.

Objectives: Delirium is common neuropsychiatric condition among elderly inpatients. The clock drawing test (CDT) has been used widely as bedside screening tool in assessing cognitive impairment in elderly people. Previous studies which evaluate its usefulness in delirium reported conflicting results. The objective of this study was to evaluate the utility of CDT to detect delirium in elderly medical patients.

Method: Prospective, observational, longitudinal study. All acute medical admissions 70 years of age and above were approached within 72 hours of admission for recruitment. Patients eligible for inclusion were assessed four times, twice weekly during admission. Assessment included Confusion Assessment Method (CAM), Delirium Rating Scale (DRS-98R), Montreal Cognitive Assessment (MoCA), Acute Physiology and Chronic Health Evaluation II (APACHE) II, and CDT. Data was analysed using a linear mixed effect model.

Results: Three hundred and twenty-three assessments with the CDT were performed on 200 subjects (50% male, mean age 81.13; standard deviation: 6.45). The overall rate of delirium (CAM+) during hospitalisation was 23%. There was a significant negative correlation between the CDT and DRS-R98 scores (Pearson correlation r = -0.618, p < 0.001), CDT and CAM (Spearman's rho = -0.402, p < 0.001) and CDT and total MoCA score (Pearson's r = 0.767, p < 0.001). However, when the data were analysed longitudinally controlling for all the factors, we found that cognitive function and age were significant factors associated with CDT scores (p < .0001): neither the presence nor the severity of delirium had an additional significant effect on the CDT.

Conclusion: CDT score reflects cognitive impairment, independently of the presence or severity of delirium. The CDT is not a suitable test for delirium in hospitalised elderly patients.