Chronic kidney disease and GFR staging

Chronic kidney disease is nephron-mass loss: total GFR is the per-nephron filtration times the remaining fraction. Stepping that fraction down walks total GFR through the KDIGO stages — 90/60/45/30/15 mL/min — while per-nephron autoregulation stays flat at each level (open loop does not). Grade [V]; KDIGO anchor [L].

CKD scales the autoregulated single-kidney GFR by the surviving nephron fraction (the intact-nephron hypothesis). The fraction steps total GFR through the KDIGO G-categories while the tubuloglomerular plateau stays flat at each reduced level (coefficient of variation ~0); the open loop instead tracks pressure (coefficient of variation 0.63).

Stage is nephron mass, not a broken loop

A reduced filtration coefficient per nephron is compensated by tubuloglomerular feedback (the surviving nephrons hyperfilter), so it cannot by itself lower the plateau without saturating the controller. What lowers the stage is loss of nephron number: total GFR is the per-nephron autoregulated value times the remaining fraction N.

Walking the KDIGO ladder

Holding per-nephron autoregulation intact and stepping N down, total GFR lands on the KDIGO thresholds — N=0.72→90, 0.48→60, 0.36→45, 0.24→30, 0.12→15 mL/min (categories G2 through G5) — and at every reduced level GFR is still flat across 80–180 mmHg (coefficient of variation ~0). The contrast is decisive: with the loop open, GFR tracks pressure with a coefficient of variation of 0.63. So CKD here is a lower autoregulated plateau, faithful to the KDIGO 2012/2024 categories; absolute stage prevalence needs population data and stays [O].