Baseline characteristics of the study population.

Abbreviations: No. Number of participants. a Three levels of comorbidity was created based on the modified Charlson comorbidity index score (m-CCI) at the date of first treatment with renal replacement therapy “Low” (CCI = 0), “Medium” CCI 1–2, and “High” CCI > 2. See text for details. b Index date: Date of first treatment (hemodialysis) for end-stage renal disease and date of sampling for population controls. c For each patient on chronic hemodialysis, 19 persons from the background population were sampled matched on age, gender, and municipality. Baseline characteristics of the study population.