Chronic kidney disease is staged by filtration rate into six GFR categories, from G1 with normal function down to G5, kidney failure. The stage steers monitoring frequency, drug dosing and referral timing, and combines with the albumin ratio to form the full KDIGO risk grid. Enter an estimated or measured GFR to see its category and what each stage typically involves.
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Kidney function does not fail overnight. It slides along a continuum that medicine slices into categories so that decisions, how often to check labs, when to adjust drug doses, when to prepare for dialysis, can be standardized. The KDIGO system uses estimated filtration as its backbone, dividing the range into G1 through G5 with a split at G3.
The Six Categories
G1 means filtration at ninety or above, normal or even high, and only counts as disease when other damage markers such as albuminuria are present. G2 covers sixty to eighty nine with the same caveat. G3a, forty five to fifty nine, is where many guidelines begin calling it chronic kidney disease outright, and G3b, thirty to forty four, halves the remaining category again because complications accelerate here. G4, fifteen to twenty nine, triggers preparation for possible replacement therapy, and G5 below fifteen is kidney failure.
Why G3 Got Split
Pooled cohort data showed risk does not move smoothly across the old stage three band. Patients at forty five face markedly more anemia, bone disease, hospitalization and death than those at fifty nine. The a and b split forces the difference into the open so that the lower half receives intensified monitoring rather than annual reassurance.
Stage Is Only Half the Grid
Prognosis sharpens when the albumin categories A1 to A3 join the GFR stage, forming the color coded KDIGO heat map. A patient at G3a with heavy albuminuria can carry higher risk than one at G4 without it, which is why modern charts plot both axes.
A single low reading does not stage anyone. Guidelines require the reduction to persist at least three months, or be backed by structural evidence, before the chronic label applies.