Presently the KDOQI Staging system for CKD (see figure) is what is used most commonly to classify the severity of reduced renal function. This is based purely on an estimation of the GFR, using equations such as the MDRD to determine GFR. While this is helpful in identifying potential patients who will go on to develop ESRD--current recommendations state that individuals with CKD Stage 3 and above be referred to a nephrologist for evaluation--there is a substantial fraction of individuals who meet the criteria for CKD Stage 3 or 4 who will never go on to develop ESRD.
An interesting paper in this month's JASN by Hallan et al suggests an alternative staging system: instead of using only eGFR, the authors define a strategy whereby eGFR is combined with the degree of albuminuria to arrive at a new classification system. They arrived at this strategy by looking at over 65,000 adults from an older large-scale health screening study (HUNT2) and determining what factors best predicted the development of ESRD. The authors argue that their newer CKD staging system is much more efficient at identifying patients truly at risk for developing ESRD compared to the traditional KDOQI system.
They calculate that referring all patients with CKD Stage 3 or above to a nephrologist would lead to working up 4.7% of the general population
Which would identify 69% of all patients who progress to ESRD.
Using their own classification scheme, however, they claim that they would need to refer only about 1.4% of the general population without sacrificing sensitivity: they estimate that they would still identify about 66% of individuals who would go on to develop ESRD.