The CDR ("Clinical Dementia Rating") scale is a questionnaire that doctors use to assess the degree of Alzheimer's disease in patients. It was developed with the aim of monitoring Alzheimer’s-related changes over time.
Doctors use the CDR scale to find out whether a patient's memory and thinking skills have got worse and how that affects their independence in everyday life. The doctor asks the questions in a personal interview with the patient and someone the patient is close to. This can be a relative, a good friend or a caregiver, for example.
The interview takes about 30 minutes.
To assess the effects of Alzheimer's disease, the CDR scale contains various questions about the patient's thinking and memory skills (cognition) and their ability to cope in everyday life (function).
The questions on cognition relate to these three categories:
The questions on function in everyday life relate to these three categories:
Based on the interview and answers, the doctor gives a score for each category: Is there no impairment or a questionable, mild, moderate or severe impairment? The score for no impairment ("none") is 0, and the score for a severe impairment is 3.
The higher the score, the more the patient's daily life is affected. The following overview can help you understand how the loss of skills in the various categories can affect everyday life.
The scores determined in the interview provide information about the degree of Alzheimer's disease.
One common evaluation approach is known as the “CDR-Sum of Boxes” (CDR-SB). Here, all of the scores are added together to arrive at an overall CDR-SB score. Because the highest score for each of the six categories is 3, the total CDR-SB score ranges between 0 and 18.
This means: The higher the score, the more the disease is causing problems and impairments.
The degree of Alzheimer's disease severity is usually assessed based on the CDR-SB score, like this:
Institute for Quality and Efficiency in Health Care (IQWiG, Germany). General Methods; Version 7.0 [online]. 2023.
Institute for Quality and Efficiency in Health Care (IQWiG, Germany). Lecanemab (early Alzheimer’s disease) – Benefit assessment according to §35a Social Code Book V. Dossier assessment; Commission A25-111 [online]. 2025.
O'Bryant SE, Waring SC, Cullum CM et al. Staging dementia using Clinical Dementia Rating Scale Sum of Boxes scores: a Texas Alzheimer's research consortium study. Arch Neurol 2008; 65(8): 1091-1095.
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