The impact of body mass index (BMI) and body weight on hospitalization rates in haemodialysis patients is unknown. This study hypothesizes that being either underweight or obese is associated with a higher hospitalization rate. Observational study of 6296 European haemodialysis patients with prospective data collection and follow-up every six months for three years (COSMOS study). The risk of being hospitalized was estimated by a time-dependent Cox regression model and the annual risk (incidence rate ratios, IRR) by Poisson regression. We considered weight loss, weight gain and stable weight. Weight change analyses were also performed after patient stratification according to their baseline BMI. A total of 3096 patients were hospitalized at least once with 9731 hospitalizations in total. The hospitalization incidence (fully adjusted IRR 1.28, 95% CI [1.18-1.39]) was higher among underweight patients (BMI <20kg/m2) than patients of normal weight (BMI 20-25kg/m2), while the incidence of overweight (0.88 [0.83-0.93]) and obese patients (≥30kg/m2, 0.85 [0.79-0.92]) was lower. Weight gain was associated with a reduced risk of hospitalization. Conversely, weight loss was associated with a higher hospitalization rate, particularly in underweight patients (IRR 2.85 [2.33-3.47]). Underweight haemodialysis patients were at increased risk of hospitalization, while overweight and obese patients were less likely to be hospitalized. Short-term weight loss in underweight individuals was associated with a strikingly high hospitalization rate.

2nd Department of Medicine and Nephrological Center University Medical School of Pécs Pécs Hungary

Centre Hospitalier FH Manhes France

CNR National Research Council Clinical Epidemiology and Physiopathology of Renal Disease and Hypertension and Renal and Transplantation Unit Ospedali Riuniti Italy

Department of Nephrology Dialysis and Renal Transplant Alessandro Manzoni Hospital Lecco Italy

Department of Nephrology Guy's and St Thomas' NHS Foundation Hospital King's Health Partners London UK

Division of Nephrology Klinikum Coburg Coburg Germany

Divisions of Renal Medicine and Baxter Novum Karolinska Institutet Sweden

Hospital Universitario de Salamanca IECSCYL Instituto Biosanitario de Salamanca Salamanca Spain

Institute Clin Exp Medicine Prague Czech Republic

Nephrology Department Hospital Curry Cabral and Faculdade de Ciências Médicas Universidade Nova de Lisboa Portugal

RWTH Aachen University Department of Nephrology and Clinical Immunology Aachen Germany

UGC Metabolismo Óseo Instituto de Investigación Sanitaria del Principado de Asturias REDinREN del ISCIII Hospital Universitario Central de Asturias Universidad de Oviedo Oviedo Asturias Spain

University Department of Nephrology Hippokration General Hospital Thessaloniki Greece

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