Comorbidity count predicted hospital disability only in the non-frail

Design

Retrospective multicentre cohort

Population

1,299 adults aged ≥65 admitted to acute hospitals in Japan, 2019–2025

Primary outcome

Hospital-associated disability (Barthel Index fall ≥5 points)

Effect

Charlson OR 1.44 (1.20–1.73) non-frail; 0.98 (0.90–1.06) frail; interaction P < 0.001

This retrospective multicentre cohort studied 1,299 adults aged 65 and over admitted to acute hospitals in Japan between 2019 and 2025. Comorbidity was measured with the Charlson Comorbidity Index and frailty with the Clinical Frailty Scale; hospital-associated disability was a fall of 5 or more points on the Barthel Index during admission.

In non-frail patients (CFS 1–3), each point on the Charlson index was associated with higher odds of hospital-associated disability (OR 1.44, 95% CI 1.20 to 1.73). In the mildly frail (CFS 4) the association weakened (OR 1.11), and in the frail (CFS 5 or more) it disappeared (OR 0.98). The difference between groups was statistically clear (P for interaction < 0.001).

For the ward, the implication is that comorbidity counts tell you little about who will lose function once a patient is already frail — every frail patient is at risk. A Clinical Frailty Scale score on admission is quick and identifies the group in whom mobility, nutrition and delirium prevention should start on day one, regardless of diagnosis list.

• Record a Clinical Frailty Scale score on admission for every patient aged 65 or over.
• Treat all frail patients (CFS 5 or more) as at high risk of losing function, whatever their comorbidity count.
• Start mobilisation, nutrition and delirium prevention from the first day in frail patients.
• Measure baseline function, such as the Barthel Index, at admission so decline can be detected.
• Use comorbidity scores mainly to stratify risk in patients who are not yet frail.

Why it matters

It challenges the habit of judging inpatient risk by the length of the problem list.

Don't overread it

A retrospective Japanese cohort — it does not show that acting on frailty scores prevents hospital-associated disability.

The statistics, in plain English

An OR of 1.44 per Charlson point in the non-frail means each extra point was linked to about 44% higher odds of disability. In the frail, an OR of 0.98 with an interval of 0.90 to 1.06 means no association. The significant interaction means this difference between groups is unlikely to be chance.

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