In chronic kidney disease staging the use of the chronicity criterion affects prognosis and the rate of progression

The Kidney Disease Outcomes Quality Initiative definition and staging of chronic kidney disease (CKD) have been adopted by most nephrologists but include a criterion of chronicity that has not been investigated. This criterion specifies that renal structural damage and/or reduction in glomerular filtration rate (GFR) should be present for periods lasting longer than 3 months. We examined the effects of changing this criterion to 6, 9, or 12 months on the prognosis and the rate of progression in population-based cohorts with CKD stages 3 and 4. A 12-month chronicity criterion significantly reduced the number of CKD patients relative to the 3-month criterion for both stages 3 and 4. For both stages, there were statistically significant differences in 5-year mortality between the 6- and 9-month cohorts. For stage 4, the 5-year cumulative incidence of renal failure significantly increased from 6 to 9 months, and the rate of change in GFR significantly decreased between the same two cohorts. The 5-year cumulative incidence of improvement in GFR lasting 1 year or more was significantly higher for the 3-month cohort than for the 12-month cohort in the stage 3 group. Hence, we suggest that the chronicity criterion is an important determinant of the characteristics of the population of patients with CKD stages 3 and 4. This may have practical consequences in both research and clinical work.