BACKGROUND: Data on comorbidities in children on kidney replacement therapy (KRT) are scarce. Considering their high relevance for prognosis and treatment, this study aims to analyse the prevalence and implications of comorbidities in European children on KRT. METHODS: We included data from patients <20 years of age when commencing KRT from 2007 to 2017 from 22 European countries within the European Society of Paediatric Nephrology/European Renal Association Registry. Differences between patients with and without comorbidities in access to kidney transplantation (KT) and patient and graft survival were estimated using Cox regression. RESULTS: Comorbidities were present in 33% of the 4127 children commencing KRT and the prevalence has steadily increased by 5% annually since 2007. Comorbidities were most frequent in high-income countries (43% versus 24% in low-income countries and 33% in middle-income countries). Patients with comorbidities had a lower access to transplantation {adjusted hazard ratio [aHR] 0.67 [95% confidence interval (CI) 0.61-0.74]} and a higher risk of death [aHR 1.79 (95% CI 1.38-2.32)]. The increased mortality was only seen in dialysis patients [aHR 1.60 (95% CI 1.21-2.13)], and not after KT. For both outcomes, the impact of comorbidities was stronger in low-income countries. Graft survival was not affected by the presence of comorbidities [aHR for 5-year graft failure 1.18 (95% CI 0.84-1.65)]. CONCLUSIONS: Comorbidities have become more frequent in children on KRT and reduce their access to transplantation and survival, especially when remaining on dialysis. KT should be considered as an option in all paediatric KRT patients and efforts should be made to identify modifiable barriers to KT for children with comorbidities.

Department of Medicine Holbæk Hospital Holbæk Denmark

Department of Nephrology and Kidney Transplantation Children's Memorial Health Institute Warsaw Poland

Department of Nephrology University Children's Hospital University of Belgrade Belgrade Serbia

Department of Paediatric Nephrology Medical University of Lublin Lublin Poland

Department of Pediatric Nephrology and Transplantation New Children's Hospital University of Helsinki and Helsinki University Hospital Helsinki Finland

Department of Pediatric Nephrology Emma Children's Hospital Amsterdam University Medical Center University of Amsterdam Amsterdam The Netherlands

Department of Pediatric Nephrology Gaziantep University Medical Faculty Gaziantep Turkey

Department of Pediatric Nephrology University Hospital Motol Prague Czech Republic

Department of Pediatrics Bordeaux University Hospital Bordeaux Population Health Research Center UMR 1219 University of Bordeaux Bordeaux France

Department of Pediatrics Medical University Graz Graz Austria

Department of Pediatrics Rouen University Hospital Rouen France

Department of Pediatrics University of Szeged Szeged Hungary

Division of Paediatric and Adolescent Medicine Department of Specialised Medicine and Transplantation Oslo University Hospital Rikshospitalet Oslo Norway

Division of Pediatric Nephrology University Medical Center Hamburg Eppendorf Hamburg Germany

Division of Pediatrics Department of Medicine University of Udine Udine Italy

ESPN ERA Registry Amsterdam UMC University of Amsterdam Department of Medical Informatics Amsterdam Public Health Research Institute Amsterdam The Netherlands

Moscow Regional Research and Clinical Institute named after M F Vladimirskiy Moscow Russia

Pediatric Department National Institute of Children's Health Comenius University Bratislava Slovakia

Pediatric Nephrology Dialysis and Transplant Unit Fondazione IRCSS Ca' Grande Ospedale Maggiore Policlinico Milan Italy

Pediatric Nephrology Unit 1st Department of Pediatrics Aristotle University of Thessaloniki Thessaloniki Greece

Pediatric Nephrology Unit Hospital Pediátrico Centro Hospitalar Universitário de Coimbra Coimbra Portugal

Pediatric Nephrology Unit University Children's Hospital Zurich Zurich Switzerland

Pediatric Uro Nephrology Center Queen Silvia Children's Hospital Sahlgrenska Academy at the University of Gothenburg Gothenburg Sweden

Population Health Sciences University of Bristol Medical School Bristol UK

UK Renal Registry Bristol UK

Univeristy of Medicine of Tirana Public Health Tirana Albania

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