1. ¹Department of Nephrology, University Hospital of North Norway, Tromsø, Norway
2. ²Department of Medical Biochemistry, University Hospital of North Norway, Tromsø, Norway
3. ³Department of Medical Biochemistry, Institute of Medical Biology, University of Tromsø, Tromsø, Norway

Correspondence: BO Eriksen, Department of Nephrology, University Hospital of North Norway, 9038 Tromsø, Norway. E-mail: bjorn.odvar.eriksen@unn.no

Received 10 November 2006; Revised 13 May 2007; Accepted 13 June 2007; Published online 8 August 2007.

Abstract

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.