Invited commentary: defining incident chronic kidney disease in epidemiologic study settings.

Chronic kidney disease affects an estimated 31 million Americans and potentially poses a significant global health and socioeconomic crisis. Chronic kidney disease can be treated if patients are identified early enough in the evolution of their kidney disease. However, in order for this to occur, suitable definitions of what is meant by "chronic kidney disease" need to be identified. In clinical practice, prevalent chronic kidney disease is diagnosed in a patient on the basis of the presence of persistent albuminuria and/or reduced glomerular filtration rate. However, it is unclear how to best define an incident of chronic kidney disease when the definition relies on the need for a patient to be seen multiple times over an extended period of time. In this issue of the Journal, Bash et al. (Am J Epidemiol. 2009;170(4):414-424) have compared 4 different definitions of incident chronic kidney disease and their agreement, incident rates, and association with known risk factors. This study explores an extremely important topic for longitudinal epidemiology studies of chronic kidney disease.