Variable selection under multiple imputation using the bootstrap in a prognostic study

Background: Missing data is a challenging problem in many prognostic studies. Multiple imputation (MI) accounts for imputation uncertainty that allows for adequate statistical testing. We developed and tested a methodology combining MI with bootstrapping techniques for studying prognostic variable selection. Method: In our prospective cohort study we merged data from three different randomized controlled trials (RCTs) to assess prognostic variables for chronicity of low back pain. Among the outcome and prognostic variables data were missing in the range of 0 and 48.1%. We used four methods to investigate the influence of respectively sampling and imputation variation: MI only, bootstrap only, and two methods that combine MI and bootstrapping. Variables were selected based on the inclusion frequency of each prognostic variable, i.e. the proportion of times that the variable appeared in the model. The discriminative and calibrative abilities of prognostic models developed by the four methods were assessed at different inclusion levels. Results: We found that the effect of imputation variation on the inclusion frequency was larger than the effect of sampling variation. When MI and bootstrapping were combined at the range of 0% (full model) to 90% of variable selection, bootstrap corrected c-index values of 0.70 to 0.71 and slope values of 0.64 to 0.86 were found. Conclusion: We recommend to account for both imputation and sampling variation in sets of missing data. The new procedure of combining MI with bootstrapping for variable selection, results in multivariable prognostic models with good performance and is therefore attractive to apply on data sets with missing values

Absence of Intragraft B Cells in Rejection Biopsies After Rituximab Induction Therapy: Consequences for Clinical Outcome

Background. The pathophysiological role of intragraft B cells during renal allograft rejection is unclear. Methods. We studied B-cell infiltration during acute rejection in 53 patients who participated in a clinical trial in which adult renal transplant patients were randomized between a single intraoperative dose of rituximab (375 mg/m(2)) or placebo as induction therapy. Two independent pathologists scored all biopsies in a blinded fashion according to the Banff classification and scored for the presence of B cells and plasma cells using CD79a and CD138 as markers. Results. The majority of acute rejections were T cell-mediated. The proportion of acute rejections with an antibody-mediated component tended to be lower in rituximab-treated patients (4/23, 17.4%) than in placebo-treated patients (11/30, 36.7%; P = 0.14). Biopsies of rituximab-treated patients had significantly lower scores for B cells (0.00; range, 0.00-0.50 vs 1.70; range, 0.60-3.30; P < 0.0001) and plasma cells (0.10; range, 0.00-1.90 vs 0.40; range, 0.00-7.50; P = 0.006). During acute rejection, intragraft clusters of B cells were not observed after rituximab induction therapy. However, the depletion of intragraft B cells during acute rejection did not affect steroid resistance, proteinuria, graft function at 2 years follow-up, or patient and graft survival at a median follow-up of 4.1 years (range, 2.0-6.2 years). Conclusions. These data do not support a harmful influence of intragraft B cells present during acute allograft rejection on the clinical course within the first few years after renal transplantation

Risk of Nephrotic Syndrome for Non-Steroidal Anti-Inflammatory Drug Users

BACKGROUND AND OBJECTIVES: Nonsteroidal anti-inflammatory drugs (NSAIDs) have been associated with AKI. Their association with nephrotic syndrome has not been systematically studied. This study aimed to assess the risk of nephrotic syndrome associated with NSAID use. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: A matched case-control study was performed in the UK primary care database. Cases were patients with a first diagnosis of nephrotic syndrome and controls were those without nephrotic syndrome. NSAID exposure (grouped either based on cyclooxygenase enzyme selectivity and chemical groups) was classified as either current (use at the nephrotic syndrome diagnosis date and corresponding date in the control group), recent, or past use. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated using unconditional logistic regression analysis. RESULTS: We included 2620 cases and 10,454 controls. Compared with non-use, current use of 15-28 days and >28 days of conventional NSAIDs was associated with a higher relative risk of nephrotic syndrome: adjusted OR, 1.34; 95% CI, 1.06 to 1.70, and OR, 1.42; 95% CI, 0.79 to 2.55, respectively. Also, recent use (discontinuation 1-2 months before nephrotic syndrome diagnosis date; OR, 1.55; 95% CI, 1.11 to 2.15) and past use (discontinuation 2 months-2 years; OR, 1.24; 95% CI, 1.07 to 1.43), but not current use of 2 years; OR, 0.96; 95% CI, 0.85 to 1.09) were associated with a higher relative risk of nephrotic syndrome as well as past use of selective COX-2 inhibitors (discontinuation 2-24 months; OR, 1.24; 95% CI, 0.98 to 1.58). Categorization based on chemical groups showed that acetic acid and propionic acid derivatives were associated with a higher risk of nephrotic syndrome. CONCLUSIONS: The use of conventional NSAIDs was associated with a higher risk of nephrotic syndrome starting from at least 2 weeks of exposure, as well as for recent and past exposure up to 2 years before the diagnosis of nephrotic syndrome. This higher risk appeared mainly attributable to acetic acid and propionic acid derivatives

Effect of a Single Intraoperative High-Dose ATG-Fresenius on Delayed Graft Function in Donation After Cardiac-Death Donor Renal Allograft Recipients:A Randomized Study

<p>Objectives: Reducing the incidence of delayed graft function after transplant with donation after cardiac death donor renal allografts would facilitate managing recipients during their first weeks after a transplant. To reduce this incidence, in most studies, induction therapy with depleting anti-T-lymphocyte antibodies is coupled with a reduction of the dosage of the calcineurin inhibitor. The separate effect of anti-T-cell therapy on the incidence and duration of delayed graft function is therefore difficult to assess.</p><p>Patients and Methods: We performed a randomized study to evaluate the effect of a single intraoperative high-dose of anti-T-lymphocyte immunoglobulin (ATG)-Fresenius (9 mg/kg body weight) on the incidence of delayed graft function. Eligible adult recipients of a first donation after cardiac death donor renal allograft were randomly assigned to ATG-Fresenius or no induction therapy. Maintenance immunosuppression consisted of tacrolimus, in an unadjusted dose, mycophenolate mofetil, and steroids.</p><p>Results: The study was prematurely terminated because of a lower-than-anticipated inclusion rate. Baseline characteristics were comparable in the ATG-Fresenius group (n=28) and the control group (n=24). Twenty-two patients in the ATG-Fresenius group (79%) had delayed graft function, compared with 13 in the control group (54%; P=.06). Allograft and patient survival were comparable in both groups. Serious adverse events occurred more frequently in the ATG-Fresenius group than they did in the control group (57% vs 29%; P <.05).</p><p>Conclusions: Intraoperative administration of a single high-dose of ATG-Fresenius in donation after cardiac death donor renal allograft recipients, followed by triple immunosuppression with an unadjusted tacrolimus dose, seems ineffective to reduce the incidence of delayed graft function. Moreover, this was associated with a higher rate of serious adverse events (EudraCT-number, 2007-000210-36.)</p>