The clock drawing test is an important contribution to the Mini Mental State Examination in screening for cognitive impairment.

Background: The clock drawing test (CDT) and the Mini Mental State Examination (MMSE) are frequently used screening instruments for cognitive impairment, however, the precise contribution of the CDT to the MMSE is largely unknown. Methods: We studied patients with subjective cognitive impairment (SCI, n = 481), mild cognitive impairment (MCI, n = 628) and Alzheimer's disease (AD, n = 1099). Discrimination between patients was examined with multiple logistic regression, adjusted for age, sex, and education. Four groups were constructed based on a normal/abnormal MMSE (cut‐off <24/30) versus normal/abnormal CDT (cut‐off ≤2/3). Visually rated medial temporal lobe atrophy (MTA) on CT was used as parameter of neurodegeneration. Results: The CDT significantly contributed to the MMSE in discriminating SCI from both MCI and AD patients. Our four group analyses showed that of those patients with a normal MMSE and incorrectly classified as SCI, an abnormal CDT could significantly identify 10.0% as MCI and 13.2% as AD. Among those with an abnormal MMSE, the percentage AD patients shifted from 53.1% to 82.1% due to an abnormal CDT. Presence of an abnormal CDT was significantly related to MTA increase, regardless of the MMSE score. Conclusion: The CDT is an important additional screening tool to the MMSE. An abnormal CDT with a normal MMSE is an indicator for cognitive impairment. An abnormal CDT in combination with an abnormal MMSE can be considered as an indicator of disease progression. Key points: The clock drawing test (CDT) is widely used as a screening tool for cognitive impairment, often in combination with the Mini Mental State Examination (MMSE), however, very few studies focus on the specific contribution of the CDT when the MMSE is known.To our knowledge, our study is the first to examine the additional value of the CDT to the MMSE in a large elderly memory clinic population to differentiate patients with mild cognitive impairment (MCI) and Alzheimer's disease (AD) from those with subjective cognitive impairment (SCI). We focus on the clinical use of both tests using predefined cut‐off scores.When patients have an MMSE of 24 or higher, and are thus classified as having no cognitive impairment by the MMSE, the CDT can significantly identify close to 25% as having either MCI or AD. When the MMSE is below 24, the combination with an abnormal CDT yielded a percentage of 82% AD.When the MMSE is known, an abnormal CDT can give additional information on progression along the SCI‐MCI‐AD trajectory. We therefore recommend the CDT as a highly relevant, quick and easy to administrate screening tool. [ABSTRACT FROM AUTHOR]