Early change in proteinuria as a surrogate outcome in kidney disease progression: a systematic review of previous analyses and creation of a patient-level pooled dataset.

BACKGROUND: Proteinuria is a candidate surrogate end point for randomized controlled trials (RCTs) in chronic kidney disease (CKD). There is a reasonably sound biological basis for this hypothesis, but only preliminary empirical evidence currently exists.
METHODS: A systematic review and creation of a patient-level dataset of randomized controlled trials (RCTs) in CKD that reported changes in proteinuria and assessed progression of kidney disease as defined by dialysis, transplantation, death, or changes in GFR or creatinine were performed.
RESULTS: Systematic review. Seventy RCTs met the eligibility criteria; 17 eligible RCTs contained analyses of proteinuria as a predictor of outcomes; 15 RCTs concluded that greater proteinuria was associated with adverse outcomes. A majority were studies of diabetic or hypertensive kidney disease and tested renin-angiotensin system blockade. Definitions of predictor and outcome variables were too variable to conduct a meta-analysis of group data. Database creation. Over 4 years was required to create the patient-level dataset. The final dataset included 34 studies and > 9000 patients with a variety of CKD types and interventions.
CONCLUSIONS: There are a relatively small number of RCTs designed to rigorously test therapies for kidney disease progression. Current analyses of change in proteinuria as a predictor of CKD progression are heterogeneous and incomplete, indicating further evaluation in a pooled individual patient-level database is necessary to advance knowledge in this field.