Diagnostic Performance of Clock Drawing Test by CLOX in an Asian Chinese population

Clock Drawing Tests are commonly used for cognitive screening, but their clinical utility has not yet been studied in Chinese Singaporeans. We examined the usefulness of a Clock Drawing Test, CLOX, in detecting dementia in our population and explored its performance in the dementia subtypes, Alzheimer's disease (AD), and the vascular composite group (VCG) of AD with cerebrovascular disease and vascular dementia.

CLOX was administered to 73 subjects (49.3%) with dementia and 75 healthy controls (50.7%). Receiver operating characteristic analysis determined the diagnostic accuracy and optimal cut-off scores, stratified by education. Analysis of Variance was used to compare CLOX scores between AD and VCG.

The diagnostic accuracy (area under the curve) was 84 and 85% for CLOX1 and CLOX2, respectively. Cut-offs at 10 for CLOX1 and 12 for CLOX2 yielded sensitivities of 75.3 and 75%, and specificities of 76 and 80%, respectively. The mean CLOX1 but not CLOX2 scores for AD (8.1) and VCG (5.5) remained significantly different (p = 0.002) after adjustment for the covariates age, gender, education, MMSE and dementia stage.

Our results support CLOX as a valid cognitive screen in Singaporean Chinese with adequate psychometric properties. In addition, CLOX may aid as an adjunct in differentiating AD from dementia with a vascular element, e.g. AD with cerebrovascular disease and vascular dementia.