Introduction: Chronic kidney disease (CKD) is a risk factor for acquiring severe COVID-19, but underlying mechanisms are unknown. We aimed to study the risk associated with CKD for severe COVID-19 outcomes in relation to body mass index (BMI) and diabetes because they are common risk factors for both CKD and severe COVID-19. Methods: This nationwide case-control study with data from mandatory national registries included 4684 patients (cases) admitted to the intensive care units (ICUs) requiring mechanical ventilation and 46,840 population-based controls matched by age, sex, and district of residency. Logistic regression was used to calculate odds ratios (ORs) with 95% confidence intervals (CIs) for associations between severe COVID-19 and exposures with adjustment for confounders, in subgroups by BMI, and matched by type 2 diabetes. Results: The median age was 64 years, and 27.7% were female. CKD was observed in 5.4% of the cases and 1.5% of the controls, whereas 1.9% and 0.3% had end-stage CKD, respectively. CKD was associated with severe COVID-19 (OR, 2.20 [95% CI, 1.85-2.62]), continuous renal replacement therapy (CRRT) in ICU (OR, 7.36 [95% CI, 5.39-10.05]), and death any time after ICU admission (OR, 2.51 [95% CI, 1.96-3.22]). The risk associated with CKD for severe COVID-19 did not differ significantly by weight but was higher in those without diabetes (OR, 2.76 [95% CI, 2.15-3.55]) than in those with diabetes (OR, 1.88 [95% CI, 1.37-2.59]). Conclusion: CKD, especially end-stage CKD, is an important risk factor for severe COVID-19 and death after ICU admission also in patients with normal BMI and without type 2 diabetes.
