Using datasets to ascertain the generalizability of clinical cohorts: the example of the European QUALity study on the treatment of advanced chronic kidney disease.

BACKGROUND: Cohort studies are among the most robust of observational studies but have issues with external validity. This study assesses threats to external validity (generalizability) in the European QUALity (EQUAL) study, a cohort study of people >65 years of age with Stage 4/5 chronic kidney disease. METHODS: Patients meeting the EQUAL inclusion criteria were identified in The Health Improvement Network database and stratified into those attending renal units, a secondary care cohort (SCC) and a not primary care cohort (PCC). Survival, progression to renal replacement therapy (RRT) and hospitalization were compared. RESULTS: The analysis included 250, 633 and 2464 patients in EQUAL, PCC and SCC. EQUAL had a higher proportion of men compared with PCC and SCC (60.0% versus 34.8% versus 51.4%). Increasing age ≥85 years {odds ratio [OR] 0.25 [95% confidence interval (CI) 0.15-0.40]} and comorbidity [Charlson Comorbidity Index ≥4, OR 0.69 (95% CI 0.52-0.91)] were associated with non-participation in EQUAL. EQUAL had a higher proportion of patients starting RRT at 1 year compared with SCC (8.1% versus 2.1%; P < 0.001). Patients in the PCC and SCC had increased risk of hospitalization [incidence rate ratio 1.76 (95% CI 1.27-2.47) and 2.13 (95% CI 1.59-2.86)] and mortality at 1 year [hazard ratio 3.48 (95% CI 2.1-5.7) and 1.7 (95% CI 1.1-2.7)] compared with EQUAL. CONCLUSIONS: This study provides evidence of how participants in a cohort study can differ from the broader population of patients, which is essential when considering external validity and application to local practice.

Dyslipidemia in chronic kidney disease: randomized controlled trial of colestilan versus simvastatin in dialysis patients.

AIM: We evaluated the effects of colestilan, a non-absorbed anion-exchange resin, on lipids and lipoproteins in dialysis patients. METHODS: This randomized, double-blind, double-dummy, flexible-dose study incorporating a placebo-controlled withdrawal period tested for superiority vs. placebo and non-inferiority vs. simvastatin. Dialysis patients with serum low-density lipoprotein (LDL-C) ≥ 100 mg/dL received colestilan 3 - 12 g/day or simvastatin 10 - 40 mg/day for 16 weeks, and were then re-randomized to continue active medication or receive placebo for 4 weeks. Co-primary endpoints were the percent change in serum LDL-C level during the active and placebo comparison phases. RESULTS: Colestilan was non-inferior to simvastatin for lowering serum LDL-C (mean changes -29.5% vs. -28.9%; difference 0.6%, 95% CI -5.7, 4.5). Colestilan was more effective than placebo at maintaining control of serum LDL-C levels during the withdrawal phase (mean change +4.4% vs. +41.7%; difference -37.4%; p < 0.001). Reductions in total cholesterol were similar with both drugs, but simvastatin was more effective at controlling triglyceride levels. Adverse events most commonly affected the gastrointestinal system. CONCLUSIONS: In dialysis patients, colestilan was more effective than placebo at maintaining control of serum LDL-C levels, was noninferior to simvastatin in terms of the reduction in LDL-C achieved, and was generally well tolerated.