Data collection

To allow rapid data collection for this time-sensitive topic, this study used an existing network of clinical centres with experience in collecting frailty data using the CFS for academic and service assessment purposes, with the addition of one Italian site. Data were collected across ten centres in the UK (Ysbyty Ystrad Fawr [Caerphilly], Royal Gwent Hospital [Newport], Nevill Hall Hospital [Abergavenny], Southmead Hospital Bristol [Bristol], Aberdeen Royal Infirmary [Aberdeen], Royal Alexandra Hospital [Paisley], Royal Inverclyde Hospital [Inverclyde], Salford Royal Infirmary [Salford], Glasgow Royal Infirmary [Glasgow], and the University Hospital of Wales [Cardiff]) and one Italian hospital (University Hospital of Modena Policlinico [Modena]). All hospitals admit acutely unwell people with COVID-19 except two sites (Ysbyty Ystrad Fawr and Glasgow Royal Infirmary) that receive self-referred patients and patients triaged by paramedic staff. For all sites, assessment of frailty using the CFS was routinely collected data (as per NICE recommendations). In each site the assessment of CFS in patients with COVID-19 was overseen by specialist COVID-19 megateams—in the UK, a megateam consisted of a consultant geriatrician, an emergency physician, and an intensive care consultant. For all patients with COVID-19 admitted to hospital, CFS was documented in a dedicated section on each patient's admission booklet. CFS is a quick to use assessment tool and is most reliably performed by geriatricians who use it routinely.

The study analysed routinely generated hospital data for patients with COVID-19. A standardised case report format was used for recording data collected prospectively and supplemented by patient records and drug prescription charts. Before participating, all study personnel completed specific data collection training. It was also a prerequisite for study personnel to familiarise themselves with the process of frailty assessment through use of an open-access online resource.¹⁷ Training was supervised at a local level by the site's principal investigator. Local data protection policy was followed in order to record data securely at each site. Subsequently, each site transferred anonymised data to King's College London for statistical analysis.

Demographic data for age and sex were collected. Variables for analysis were selected from those used in recent COVID studies, which appear to be prognostic indicators.^{1, 2, 4, 18} These were clinical diagnosis of coronary artery disease, diabetes, and hypertension; smoking status (never, previous, or current); and blood biomarkers (C-reactive protein, with >40 mg/dL considered abnormal; albumin, with ≤34 g/L considered hypoalbuminaemia; and estimated glomerular filtration rate [eGFR], with <60 mL/min per 1·73 m² considered moderate or worse renal function).

The CFS (appendix p 6) was used to assess frailty. It bases the frailty assessment on how a patient was 2 weeks before hospital admission. The CFS is an ordinal hierarchical scale that numerically ranks frailty from 1 to 9, with a score of 1 being very fit, 2 well, 3 managing well, 4 vulnerable, 5 mildly frail, 6 moderately frail, 7 severely frail, 8 very severely frail, and 9 terminally ill. We did not anticipate that there would be adequate number of events for each score so scores were grouped 1–2 (fit), 3–4 (becoming vulnerable, but not frail), 5–6 (initial signs of frailty but with some degree of independence), and 7–9 (severe or very severe frailty) for the purposes of the analyses. These groups were selected to fit with the clinical descriptions outlined in the CFS and we deemed them to be reasonable groupings of severity of frailty.