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Printed on 7/21/2026
For informational purposes only. This is not medical advice.
The SOF Frailty Index is a brief frailty screening tool based on 3 criteria: unintentional weight loss, inability to rise from a chair five times without using arms, and reduced energy level. It is used as a practical alternative to longer frailty phenotypes in older-adult clinical workflows.
Formula: SOF total = count of 3 frailty criteria present (range 0-3).
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The SOF Frailty Index evaluates three biologically based frailty criteria derived from the Study of Osteoporotic Fractures: (1) unintentional weight loss — defined as losing 5% or more of body weight in the past year without intentional dieting; (2) inability to rise from a chair five times without using the arms — a functional lower-extremity strength test performed at the bedside or in clinic; and (3) reduced energy — typically assessed by asking whether the patient feels full of energy on most days (a 'No' response positive for this criterion). Each criterion is scored as present (1) or absent (0). The SOF criteria are derived from objective assessments with established test-retest reliability and can be gathered in under 5 minutes by a clinician, nurse, or trained allied health professional during a routine outpatient or inpatient encounter.
After assessing each criterion, the number of positive findings is counted. A SOF total of 0 means none of the three frailty criteria are present. A total of 1 means one criterion is positive. A total of 2 means two criteria are positive. A total of 3 means all three criteria are met. The count is the SOF Frailty Index score. Unlike longer frailty instruments that incorporate dozens of deficits, the SOF's three-item count structure is intentionally simple for fast clinical application. No weighting or algorithm is needed — the total count is the result. The brief administration time (under 5 minutes) compared to the original Fried Frailty Phenotype (which also includes grip strength and walking speed) is a key practical advantage of the SOF in busy clinical settings.
SOF scores classify older adults into three frailty categories with distinct clinical implications: 0 criteria met indicates robust (non-frail) status, associated with lowest risk of adverse outcomes; 1 criterion met indicates pre-frailty, associated with intermediate risk and the highest priority for preventive interventions to halt frailty progression; and 2 to 3 criteria met indicates frailty, associated with substantially elevated risks of falls, disability, hospitalization, and all-cause mortality. The frailty classification informs perioperative risk assessment, chemotherapy tolerance estimation, rehabilitation goal-setting, advance care planning conversations, and the intensity of preventive interventions such as exercise prescriptions, nutritional support, and medication review. In geriatric co-management models, SOF frailty status guides hospital resource allocation and discharge planning complexity.
Surgeons, anesthesiologists, perioperative nurses, surgical co-management teams
Frailty is one of the strongest independent predictors of postoperative complications, prolonged hospital stay, discharge to nursing facility, and 30-day and 90-day mortality — often outperforming chronological age and standard ASA classification for surgical risk. The SOF Frailty Index provides a rapid, three-item pre-surgical frailty screen that can be embedded into pre-anesthesia assessment workflows or surgical outpatient visits. Patients classified as frail (SOF 2–3) may benefit from prehabilitation programs (exercise, nutritional optimization, medication rationalization) initiated before elective surgery, and from enhanced perioperative monitoring, early mobilization, and comprehensive discharge planning post-operatively. For urgent or emergency surgical cases, SOF frailty status informs goals-of-care conversations with patients and families regarding expected recovery trajectory.
Medical oncologists, oncology nurses, geriatric oncologists, hematologists
Frailty is a critical determinant of chemotherapy tolerance, treatment-related adverse event risk, and overall survival in older cancer patients. Standard oncology performance scales (ECOG Performance Status, [Karnofsky Scale](/tools/ecog-performance)) often underestimate frailty-related vulnerability in older adults who appear functionally intact but are physiologically compromised. The SOF Frailty Index can be used as a rapid first-step geriatric frailty screen in oncology outpatient settings, identifying patients who warrant comprehensive geriatric assessment (CGA) before initiating potentially toxic treatments. Patients with SOF scores of 2 or 3 are at substantially higher risk of chemotherapy dose reductions, hospitalizations, and early treatment discontinuation, informing whether aggressive curative-intent treatment versus goals-of-care-aligned palliative approaches are more appropriate.
Geriatricians, geriatric nurse practitioners, internists, family physicians with geriatric panels
In geriatric medicine outpatient settings, the SOF Frailty Index serves as a fast phenotype-based frailty screen that is integrated into annual wellness visits, chronic disease management appointments, or new-patient geriatric assessments. SOF frailty status guides care planning decisions including the appropriateness of preventive interventions (exercise programs, fall prevention, nutritional assessment), the intensity of chronic disease management (glycemic targets in diabetes, blood pressure targets, polypharmacy review), advance directive conversations, and referrals to occupational therapy, physiotherapy, dietetics, or social work. Identifying pre-frail patients (SOF = 1) is particularly valuable because this population is the most likely to benefit from interventions that halt or reverse frailty progression.
Hospitalists, geriatric medicine consultants, discharge planners, social workers, physiotherapists
In the inpatient setting, the SOF Frailty Index can be rapidly applied at admission to characterize baseline frailty and guide hospitalization management. Frail patients (SOF 2–3) are at substantially elevated risk for hospital-acquired delirium, falls, functional decline, pressure injuries, aspiration pneumonia, and prolonged length of stay — risks that are amenable to structured Acute Care for Elders (ACE) unit or geriatric co-management protocols. SOF frailty status at admission informs early physiotherapy mobilization plans, nutritional supplementation orders, delirium prevention bundles, and discharge planning complexity (likelihood of needing rehabilitation, home care, or nursing facility placement rather than direct home discharge). Serial SOF assessment before and after hospitalization can track functional trajectory during the acute illness episode.
Epidemiologists, aging researchers, public health researchers, clinical trial investigators in geriatrics
The SOF Frailty Index was developed from the Study of Osteoporotic Fractures, one of the largest and most influential aging research cohorts, giving it established normative data and validated predictive validity for falls, fractures, disability, and mortality across diverse older adult populations. In population-based research, the SOF's three-item, objectively assessable structure is particularly valuable for standardized measurement across large samples, as it avoids the subjectivity inherent in clinician-rated instruments. The SOF has been widely used in clinical trials testing exercise, nutritional, hormonal, and pharmacological interventions to prevent or reverse frailty. Its conciseness also makes it suitable for repeated measurement in longitudinal cohort studies tracking frailty trajectories across years or decades of follow-up.
Robust older adults (SOF = 0) are at low immediate risk and require standard preventive care. Frail older adults (SOF 2–3) already have established frailty that requires management. Pre-frail older adults (SOF = 1) are at the critical transition point where evidence-based interventions — progressive resistance exercise, protein optimization, polypharmacy review, management of depression and sensory impairment — have the greatest potential to prevent or reverse progression to clinical frailty. Identifying pre-frail patients and enrolling them in structured preventive programs is therefore the highest clinical yield use of SOF screening. Flag SOF = 1 patients for enhanced preventive follow-up at every visit.
Of the three SOF criteria, the five-times-sit-to-stand chair rise test (inability to complete five rises from a standard chair without using arms) is the most objectively assessed, with the highest inter-rater reliability and the clearest relationship to lower extremity muscle strength, a core biological frailty component. When a patient fails the chair rise test (SOF criterion 2 positive), it directly identifies lower-extremity weakness as a modifiable target: referral to physiotherapy for progressive lower-extremity resistance training has Level A evidence for improving chair rise performance and reducing fall risk. Track chair rise performance as a specific exercise therapy outcome metric, not just as a frailty criterion.
The SOF provides a brief phenotype-based frailty score rooted in objective criteria. The [Clinical Frailty Scale (CFS)](/tools/clinical-frailty) provides a broader functional and activity-based 9-point frailty characterization that includes cognitive impairment and dependence domains absent from the SOF. In complex older patients — particularly those with cognitive impairment, dementia, or multi-domain functional decline — combining SOF with CFS provides a more complete frailty picture. SOF ≥2 + CFS ≥5 (mildly frail) represents high-risk frailty with convergent evidence from two independent frailty conceptual frameworks, supporting more intensive clinical management and goals-of-care conversations.
The three SOF criteria (weight loss, reduced energy, chair rise difficulty) can all be transiently elevated by acute illness, hospitalization, or deconditioning from a recent medical event that does not represent chronic frailty. A patient who is post-hospitalization for pneumonia may score SOF 2–3 acutely yet return to SOF 0 after 4 to 6 weeks of recovery and rehabilitation. When assessing a recently hospitalized or acutely ill older adult, explicitly ask about baseline function and energy level before the acute illness, rather than basing the SOF classification entirely on current status. Documenting baseline SOF (pre-morbid) versus current SOF allows tracking of acute-on-chronic frailty and recovery trajectory.
A SOF score of 2 to 3 indicates frailty with substantially elevated 1-year risks of disability progression, hospitalization, and mortality. This frailty characterization provides objective, prognostic context for advance care planning conversations that go beyond diagnosis-specific prognosis. Explaining frailty status to patients and families in accessible terms — 'Your body's reserves are lower than average, meaning illness or procedures carry more risk and recovery takes longer' — helps patients make informed decisions about surgery, hospitalization intensity, code status, and long-term care preferences. SOF frailty status is also a useful communication tool for goals-of-care conversations in multidisciplinary care conferences.
SOF Frailty Index was developed and validated in older-adult cohorts as a simplified frailty phenotype alternative.
Higher SOF totals indicate greater frailty burden and support comprehensive geriatric assessment.
Use when a rapid phenotype-style frailty screen is needed in clinic, inpatient, or community settings.
Binary criteria can miss nuanced functional decline and may be influenced by acute illness effects.
For related assessments, see Fried Frailty, FRAIL Scale and Clinical Frailty Scale.
Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health.
April 21, 2026 · trust-baseline
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