Grading of individual studies was done by one of the reviewers, then confirmed by another, and finalized in a group meeting. Variations of this system have been used in most KDOQI and all KDIGO guidelines and have been recommended by the US Agency for Healthcare Research and Quality Evidence-based Practice Center program.107 Each study was given an overall quality grade based on its design, methodology (randomization, allocation, blinding, definition of outcomes, appropriate use of statistical methods, etc.), conduct (dropout percentage, outcome assessment methodologies, etc.) 