Assessment of the diagnostic accuracy and discriminative validity of the Clock Drawing and Mini-Cog tests in detecting cognitive impairment.

Introduction And Objectives: The Mini-Cog is a very brief, widely used cognitive test that includes a memory task and a simplified assessment of the Clock Drawing Test (CDT). There is not a formal evaluation of the Mini-Cog test in Spanish. This study aims to analyse the diagnostic usefulness of the Mini-Cog and CDT for detecting cognitive impairment (CI).

Methods: We performed a cross-sectional study, systematically including all patients who consulted at our neurology clinic over a 6-month period. We assessed diagnostic usefulness for detecting CI (defined according to the National Institute on Aging-Alzheimer's Association criteria for mild cognitive impairment and dementia) according to the area under the receiver operating characteristic curve (AUC). Sensitivity, specificity, and positive and negative likelihood ratios were calculated for each cut-off point.

Results: The study included 581 individuals (315 with CI); 55.1% were women and 27.7% had not completed primary studies. The Mini-Cog showed greater diagnostic usefulness than the CDT (AUC ± sensitivity: 0.88 ± 0.01 vs 0.84 ± 0.01; P < .01). Both instruments were less useful for screening in individuals with a low education level (0.74 ± 0.05 vs 0.75 ± 0.05, respectively). A cut-off point of 2/3 in the Mini-Cog achieved a sensitivity of 0.90 (95% CI, 0.87-0.93) and a specificity of 0.71 (95% CI, 0.65-0.76); a cut-off point of 5/6 in the CDT achieved a sensitivity of 0.77 (95% CI, 0.72-0.81) and a specificity of 0.80 (95% CI, 0.75-0.85).

Conclusion: In our neurology clinic, the Mini-Cog showed acceptable diagnostic usefulness for detecting CI, greater than that of the CDT; neither test is an appropriate instrument for individuals with a low level of education.