The calculation of a frailty score varies depending on the assessment model used. The three most common and widely recognized methods are the Deficit Accumulation Frailty Index, the Fried Frailty Phenotype, and the Clinical Frailty Scale (CFS). Each of these tools uses a distinct set of criteria and a specific calculation to arrive at a final score.
Method 1: The Deficit Accumulation Frailty Index (FI)
The Frailty Index (FI), developed by researchers at Dalhousie University, is based on a cumulative deficit model. It quantifies frailty by counting the total number of health deficits an individual has from a pre-specified list. Deficits can include a wide range of signs, symptoms, diseases, and functional impairments.
How the FI is calculated
- Define a list of deficits: A comprehensive list of at least 30 to 40 health-related variables is established. These are typically drawn from medical history, physical exams, and lab reports.
- Score each deficit: For each item, the presence of a deficit is scored. This can be binary (0 for absence, 1 for presence) or graded (e.g., 0 for no issue, 0.5 for a partial issue, and 1 for a full deficit).
- Sum the scores: The scores for all the deficits are added together.
- Divide by the total: The sum of the deficits is divided by the total number of deficits considered, resulting in a score between 0 and 1.
Example calculation: If a patient has 10 deficits out of a list of 40 considered, their frailty index would be $10/40 = 0.25$.
Method 2: The Fried Frailty Phenotype
This method defines frailty based on the presence of five physical criteria. It is designed to identify a physical frailty phenotype and is often used in research settings.
How the Fried Phenotype is calculated
For each of the five criteria, the patient receives 1 point if they meet the threshold for a deficit:
- Unintentional weight loss: Losing 10 pounds (or >5% of body weight) in the past year unintentionally.
- Self-reported exhaustion: Consistently feeling tired or reporting low energy levels over a set period.
- Weakness (grip strength): Having a low grip strength, typically measured with a dynamometer and adjusted for sex and body mass index.
- Slow walking speed: Taking a longer time to walk a specified distance (e.g., 4 meters), with thresholds based on sex and height.
- Low physical activity: Engaging in limited physical activity, often measured via a questionnaire on energy expenditure.
Scores are then summed to classify the individual:
- Robust: 0 points
- Pre-frail: 1–2 points
- Frail: 3 or more points
Method 3: The Clinical Frailty Scale (CFS)
The CFS is a judgment-based tool used to quickly and simply assess a patient's frailty level. It relies on clinical observation and a review of medical history rather than a strict count of deficits.
How the CFS is calculated
- Observational assessment: A clinician evaluates a patient's cognitive status, functional ability, comorbidities, and mobility based on a set of nine categories.
- Assign a score: The clinician assigns a single score from 1 (very fit) to 9 (terminally ill) based on how the patient's condition matches the descriptions and pictographs.
- Classify frailty: A score of 5 or more indicates frailty, with higher scores representing increasing severity.
Comparison of Frailty Scoring Methods
| Aspect | Deficit Accumulation Frailty Index (FI) | Fried Frailty Phenotype | Clinical Frailty Scale (CFS) |
|---|---|---|---|
| Scoring Type | Continuous (0-1) | Categorical (Robust, Pre-frail, Frail) | Ordinal (1-9) |
| Assessment Method | Sum of numerous deficits (30-70+) from multiple domains. | Measurement of 5 physical criteria. | Clinical judgment based on patient observation and history. |
| Data Source | Administrative records, comprehensive geriatric assessment (CGA). | Standardized measurements and self-reported answers. | Clinician's expertise and patient records. |
| Key Strengths | Flexible, highly predictive, works with existing data. | Well-validated, good for research, objective physical measures. | Quick, easy to use, integrates clinical expertise. |
| Key Limitations | Can be cumbersome and complex, sensitive to the deficits included. | Primarily focuses on physical frailty, may require special equipment. | Subjective, depends on assessor's expertise, not for untrained staff. |
Other notable frailty scales
While the FI, Fried Phenotype, and CFS are prominent, several other scales are used for specific contexts. The FRAIL scale, for instance, is a five-question, self-reported tool based on Fatigue, Resistance, Ambulation, Illnesses, and Loss of Weight, making it a quick screening test. Another is the electronic Frailty Index (eFI), which automatically calculates a score using routine data from electronic health records, typically containing 36 deficits.
Conclusion
How a frailty score is calculated depends on the specific assessment tool used, as there is no universal formula. From the detailed deficit counting of the Frailty Index to the simple clinical grading of the Clinical Frailty Scale, each method provides a valuable but different perspective on a person's vulnerability. For clinicians, selecting the most appropriate tool depends on the setting, the patient's context, and the time available for assessment. Regardless of the method, the ultimate goal is to accurately quantify a patient's frailty to inform more personalized and effective care plans that address their unique needs.
Frailty assessment methods at a glance
- Deficit Accumulation Frailty Index: Calculate the number of accumulated health deficits divided by the total number considered. A higher score closer to 1 indicates more severe frailty.
- Fried Frailty Phenotype: Count the number of specific physical deficits (weight loss, exhaustion, weakness, slowness, low activity). A score of 3 or more classifies a person as frail.
- Clinical Frailty Scale: Use clinical judgment and a nine-point scale based on descriptions of a patient's activity and functional status. A score of 5 or higher is considered frail.
- FRAIL Scale: Use a five-question self-report to tally points for fatigue, resistance, ambulation, illnesses, and weight loss. A score of 3 or higher indicates frailty.
- Electronic Frailty Index (eFI): Employ automated calculations from electronic health records using a cumulative deficit model. Higher scores indicate greater frailty.
