Clinical Dementia Rating (CDR) Global: Definition and Clinical Application
The CDR Global is a clinician-rated measure that provides a comprehensive assessment of cognitive and functional impairment in dementia, grading severity on a scale from 0 (cognitively unimpaired) to 3 (severe dementia) based on performance across six domains: memory, orientation, judgment and problem solving, community affairs, home and hobbies, and personal care. 1
Structure and Scoring
The CDR is administered through structured interviews and examinations that evaluate both cognitive abilities (memory, orientation, judgment) and functional domains (community affairs, home activities, personal care) 1
Scoring is conducted on a 5-point scale for each domain:
- 0 = No impairment
- 0.5 = Questionable/very mild impairment
- 1 = Mild impairment
- 2 = Moderate impairment
- 3 = Severe impairment 1
The global CDR score is calculated using a standardized algorithm that weighs the memory domain more heavily than other domains, reflecting the central importance of memory impairment in dementia progression 2, 3
Clinical Applications
The CDR is widely used as a clinical trial outcome measure and research staging instrument for Alzheimer's disease and related disorders 1
The CDR Sum of Boxes (CDR-SOB) is a related metric that ranges from 0 (cognitively unimpaired) to 18 (severe global impairment) and provides more granular assessment of impairment 1
In clinical practice, the CDR has shown good correlation with activities of daily living and cognitive performance, particularly in Parkinson's Disease Dementia (PDD) 1, 3
The CDR-SOB has been validated for use in both Alzheimer's disease and Parkinson's disease and has been used as a primary outcome in trials of potential disease-modifying therapies 1
Practical Considerations
The CDR requires significant time to administer and is therefore used primarily in specialty clinical practice settings rather than primary care 1
Training is essential for reliable administration, with multicenter studies demonstrating that standardized training protocols can achieve 83% agreement with gold standard ratings 4
The CDR has excellent internal consistency (Cronbach's alpha 0.94-0.98) and interrater reliability (intraclass correlation coefficient 0.88-0.96) when properly administered 5
Electronic versions of the CDR have been developed to improve standardization and reliability in research and clinical settings 5
Limitations and Alternatives
The CDR is not familiar to many clinicians and may not be practical for routine clinical use outside specialty settings 1
Shorter screening tools like the Quick Dementia Rating System (QDRS) can be used as initial assessments, with the CDR reserved for cases where the QDRS indicates potential impairment 6
For global assessment in typical clinical practice, simpler validated tools that incorporate caregiver input may be more practical, such as the Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE) 1
The CDR should be complemented by domain-specific assessments when evaluating particular aspects of cognition or function 1