COVID-19 analysis
An additional unplanned analysis, which was added shortly after trial initiation in the setting of the COVID-19 pandemic, was to evaluate COVID-19 filters vs. non-COVID-19 filters. Given the differential anticoagulation strategies used in response to COVID-19, we also added additional unplanned analyses for anticoagulation strategy. No patients in this trial developed COVID-19 after CKRT initiation, and so all patient filters in patients who had tested positive for COVID-19 were considered COVID-positive filters. Continuous variables are reported as means and standard deviations or as medians and interquartile ranges; categorical variables are reported as frequencies and proportions. Mann-Whitney U test and chi-square test were used accordingly. Due to the significant impacts of anticoagulation and COVID-19 on filter life, additional analyses were conducted to determine if significant statistical interactions were present. We followed a backwards selection procedure to remove higher-order interactions that were not significant, resulting in a model that only had modality in it. For both the ITT and PP predictors, we fit univariate models, then added group and the modality*group interaction. Anticoagulation was stratified into heparin-only and citrate-only.