The CDR scale — short for Clinical Dementia Rating — is a standardized tool used by clinicians to measure how severely dementia is affecting a person’s daily functioning. Developed and maintained by the Knight Alzheimer Disease Research Center at Washington University in St. Louis, the CDR assigns a numeric score ranging from 0 to 3 that reflects where someone falls on the spectrum from normal cognition to severe dementia. A score of 0 means no dementia is present.
A score of 0.5 indicates very mild or questionable impairment. Scores of 1, 2, and 3 represent mild, moderate, and severe dementia respectively. If a person can still manage their finances and household but struggles to recall recent conversations, they might land at a CDR of 0.5 — a stage that carries real clinical weight even if outsiders might dismiss it as normal aging. Beyond the simple 0-to-3 global score, the CDR also produces a more detailed measure called the CDR Sum of Boxes, or CDR-SB, which captures impairment across six specific life domains. This article explains how both scoring systems work, who administers the assessment and how, and why the CDR has become one of the most important instruments in both clinical dementia care and Alzheimer’s disease research — including recent drug trials for treatments like lecanemab and donanemab.
Table of Contents
- What Is the CDR Scale and How Does It Stage Dementia?
- The Six Domains — What the CDR Actually Measures
- CDR Sum of Boxes — A More Granular Look at Severity
- How the CDR Assessment Is Conducted
- The CDR in Clinical Research — Including New Drug Trials
- How Families Encounter the CDR Scale
- The CDR’s Role in the Future of Dementia Care
- Conclusion
- Frequently Asked Questions
What Is the CDR Scale and How Does It Stage Dementia?
The CDR scale was designed to answer a deceptively difficult question: how impaired is this person, really? dementia is not a single disease but a syndrome affecting memory, reasoning, and behavior in ways that vary enormously from person to person. Clinicians needed a structured, reproducible method to describe that variability in a way that could be compared across patients, research sites, and time. The CDR provides that common language. The scale evaluates functioning across six domains: Memory, Orientation, Judgment and Problem Solving, Community Affairs, Home and Hobbies, and Personal Care. Each domain is scored individually, and a clinician then synthesizes these into a single Global CDR score. Memory carries the most weight in this process.
The resulting score places the patient at one of five levels: 0 (no dementia), 0.5 (very mild or questionable), 1 (mild), 2 (moderate), or 3 (severe). Consider someone who can no longer manage their bank accounts or plan a meal but still recognizes family members and handles basic hygiene — that profile is consistent with a CDR of 1, meaning mild dementia. One important distinction: the CDR measures functional impairment, not just cognitive test performance. A person can score poorly on a memory test in a clinic yet still function independently at home, which would affect their CDR rating. This real-world orientation is part of what makes the scale clinically meaningful. It reflects what the person can actually do, not just what they can recall under controlled conditions.
The Six Domains — What the CDR Actually Measures
Each of the six CDR domains captures a different dimension of how dementia interferes with daily life. Memory is assessed not just by asking the person questions, but by gathering information about whether they repeat themselves, forget appointments, or lose track of important items in the home. Orientation examines awareness of time, place, and personal history. Judgment and Problem Solving looks at whether someone can handle complex tasks like managing finances, making sound decisions under pressure, or recognizing when a situation is dangerous. Community Affairs covers whether the person can function independently in public — shopping, attending events, maintaining social relationships. Home and Hobbies examines the activities that once filled a person’s personal life: cooking, gardening, home repairs, reading, or any regular pursuit.
Personal Care, the final domain, assesses whether someone requires prompting or assistance with basic hygiene, dressing, and toileting. Together, these six categories paint a far more complete picture than any single test. A family member, for instance, might report that their mother still bathes herself and keeps her room tidy (Personal Care: 0) but has completely abandoned the needlework she loved for thirty years (Home and Hobbies: 1 or 2) — a pattern that has diagnostic meaning even when cognitive tests show only modest decline. However, the quality of the CDR assessment depends heavily on the reliability of the informant. If the family member providing background information is minimizing symptoms out of denial, or exaggerating them out of caregiver stress, the resulting score may not accurately reflect the patient’s actual functioning. Clinicians are trained to probe for inconsistencies and triangulate across sources, but this remains a real limitation of any assessment that relies on structured interviews rather than direct behavioral observation.
CDR Sum of Boxes — A More Granular Look at Severity
While the Global CDR score gives a useful shorthand for staging, the CDR Sum of Boxes (CDR-SB) provides considerably more detail. Each of the six domains is rated on its own scale, and the six scores are added together to produce a total ranging from 0 to 18. A score of 0 indicates no impairment across any domain. A score of 18 represents maximum impairment in all six areas. The CDR-SB is particularly valuable for tracking change over time.
A patient moving from a CDR-SB of 2.0 to 4.0 is still within the global CDR 0.5 range, but that two-point shift in the sum score reflects real deterioration that a clinician — or a family caregiver — would likely notice. Validated ranges link specific CDR-SB totals to global scores: 0.5 to 4.0 corresponds to global CDR 0.5; 4.5 to 9.0 maps to CDR 1; 9.5 to 15.5 to CDR 2; and 16.0 to 18.0 to CDR 3. Think of the global CDR as a chapter heading and the CDR-SB as the paragraph — both are necessary, but the sum score tells you more about where within that chapter the patient actually sits. This granularity is one reason the CDR-SB has become the primary endpoint in several major Alzheimer’s drug trials. Lecanemab (approved under the brand name Leqembi) and donanemab both used CDR-SB as a key measure of clinical benefit in their pivotal trials. A 2025 study published in Alzheimer’s and Dementia examined what it actually means, in practical terms, to slow the progression of CDR-SB scores with disease-modifying therapies — a question that matters enormously as these treatments move into wider clinical use.
How the CDR Assessment Is Conducted
The CDR is administered through a semi-structured interview process conducted by a trained clinician. The assessment typically takes about 30 minutes and involves two parallel conversations: one with the patient and one with a reliable informant, usually a family member or close caregiver who has regular, direct contact with the patient and can speak honestly about their daily functioning. The informant interview is not optional — it is central to the validity of the score. The clinician follows a structured protocol but is not reading from a rigid script. The semi-structured format allows the examiner to probe, clarify, and follow up on responses that seem inconsistent or unclear. This flexibility is one of the CDR’s strengths compared to purely objective cognitive batteries, but it also means results can vary if the examiner is less experienced.
The Knight ADRC at Washington University has invested substantially in training and certification to address this. Many research centers require clinicians to undergo formal CDR training and demonstrate interrater reliability before administering the scale in clinical trials. Compared to brief screening tools like the Mini-Mental State Examination (MMSE) or the Montreal Cognitive Assessment (MoCA), the CDR takes more time and requires more infrastructure. The tradeoff is depth. A brief screener can flag cognitive impairment, but it cannot tell a clinician whether the patient is still managing their household bills or whether they’ve stopped attending the community activities they once enjoyed. For research purposes and for treatment decisions involving significant interventions, that depth is often worth the additional time investment.
The CDR in Clinical Research — Including New Drug Trials
The CDR has long been a standard outcome measure in Alzheimer’s disease research, but its role has grown substantially as disease-modifying therapies have entered clinical trials. When researchers want to know whether a new drug is actually slowing the course of the disease rather than just improving test scores, they need a measure that captures real-world functional change. The CDR-SB fills that role. Both lecanemab and donanemab, the first anti-amyloid therapies to demonstrate meaningful clinical benefit in late-stage trials, used CDR-SB as a primary or co-primary endpoint. The ability of these trials to show statistically significant slowing of CDR-SB progression was central to their regulatory pathway.
This elevated the CDR from a useful clinical staging tool to a gatekeeper of drug approval — a significant shift that has prompted deeper scrutiny of what a given change in CDR-SB score actually means for a patient’s daily life. That scrutiny is well warranted. A reduction in the rate of CDR-SB progression by, say, 35% sounds compelling in a press release, but translating that into what a patient and family will actually experience over three or five years is genuinely difficult. The 2025 analysis in Alzheimer’s and Dementia addressed this directly, attempting to establish clinically meaningful thresholds for CDR-SB change — in other words, how much slowing is enough to make a real difference. This remains an evolving area of inquiry, and clinicians and patients should approach claims about CDR-SB benefits with both optimism and careful scrutiny.
How Families Encounter the CDR Scale
Most families do not encounter the CDR scale by name. A neurologist or memory care specialist may administer it as part of a comprehensive evaluation, but the results are typically communicated in plain language — “your mother is in the mild stage of Alzheimer’s” — rather than as a numeric score. Understanding that this staging is based on a structured, validated tool can be reassuring for families who wonder whether clinical descriptions of severity are based on anything rigorous.
When a loved one is being evaluated for enrollment in a clinical trial, the CDR becomes more visible. Trial eligibility criteria often specify CDR score ranges — for example, requiring a global CDR of 0.5 or 1 for trials targeting early-stage disease. If a family member has been told their loved one does not qualify for a particular study, the CDR score may be one reason. Knowing that a CDR of 2 reflects moderate dementia, and that most current trials are focused on earlier stages, helps families understand why certain trials are or are not accessible to them.
The CDR’s Role in the Future of Dementia Care
As Alzheimer’s disease research increasingly shifts toward earlier intervention — including preclinical stages where biomarkers are present but symptoms have not yet emerged — the CDR faces questions about its future relevance. The scale was designed to measure functional impairment, which means it has limited utility in people who are cognitively normal by clinical standards but carrying amyloid burden detectable by PET scan or blood-based biomarkers.
Researchers are exploring how tools like the CDR can be adapted or supplemented for these earlier populations, and whether the 0.5 category needs further refinement to distinguish meaningfully between subjective cognitive decline and very early objective impairment. What is clear is that the CDR’s core logic — assessing real-world function across multiple life domains, with input from both patient and caregiver — reflects something that more technologically sophisticated measures have not yet replaced. Its durability across decades of research suggests it captures something genuine about what it means to live with dementia.
Conclusion
The CDR scale is one of the most thoroughly validated and widely used tools in dementia care and research. It translates the complex, multidimensional reality of cognitive decline into a structured, reproducible staging system built on six functional domains. The Global CDR score offers a clear shorthand — 0.5 for very mild, 1 for mild, 2 for moderate, 3 for severe — while the CDR Sum of Boxes provides the granular detail needed to track change over time and assess the impact of treatments.
For families navigating a dementia diagnosis, understanding the CDR can demystify clinical language and help make sense of research news about new therapies. For clinicians and researchers, it remains a gold standard for staging — one that has proven robust enough to serve as a primary endpoint in the landmark trials that produced the first disease-modifying Alzheimer’s treatments. As those treatments move from trials into practice, and as research pushes further into earlier stages of disease, the CDR will continue to evolve — but its foundation in functional, real-world assessment remains its most important feature.
Frequently Asked Questions
What does a CDR score of 0.5 actually mean in practice?
A CDR of 0.5 indicates very mild or questionable dementia. The person may have consistent memory lapses, slight difficulty with complex tasks like managing finances, or a noticeable reduction in previously enjoyed activities. However, they typically remain independent in daily life. This stage is sometimes called mild cognitive impairment (MCI), though the CDR 0.5 category and MCI are not perfectly equivalent terms.
Who can administer the CDR scale?
The CDR must be administered by a trained clinician. It is not a self-administered questionnaire or caregiver checklist. Proper training is required to conduct the semi-structured interview correctly and to synthesize domain scores into an accurate global rating. Many research centers require formal certification.
How is the CDR different from the MMSE or MoCA?
The MMSE and MoCA are brief cognitive screening tests that can be administered in about 10 minutes and measure cognitive performance directly. The CDR is a functional staging tool that assesses how impairment affects daily life, using structured interviews with both the patient and a caregiver. The CDR takes about 30 minutes and provides staging information rather than a cognitive performance score.
Why is the CDR used in drug trials?
The CDR-SB is used as an outcome measure in clinical trials because it captures clinically meaningful functional change across real-world domains. When evaluating whether a drug slows the course of dementia, researchers need evidence that the benefit shows up in how people actually live — not just on cognitive tests. Both lecanemab and donanemab used CDR-SB as a primary endpoint in their pivotal trials.
Can the CDR score change over time?
Yes. CDR scores are not fixed — they are reassessed periodically to track disease progression. A person who scores 0.5 today may progress to a CDR of 1 over months or years. In research settings, tracking CDR-SB change over time is one of the primary ways clinicians measure whether a disease-modifying treatment is working.
Is a CDR of 0.5 considered dementia?
That depends on context and clinical judgment. In some frameworks, CDR 0.5 is described as “questionable” dementia or very mild impairment rather than dementia proper. In others, particularly when the impairment is consistent and supported by biomarker evidence, it may be classified as early-stage Alzheimer’s disease. The distinction matters for clinical trial eligibility and for how families understand a diagnosis.
