CKD staging (KDIGO)
Formal Definition
The KDIGO (Kidney Disease: Improving Global Outcomes) classification and staging system for chronic kidney disease — categorizes CKD by (1) Cause (etiology — e.g., diabetic nephropathy, hypertensive nephrosclerosis, polycystic kidney disease), (2) GFR category (G1: ≥90, G2: 60–89, G3a: 45–59, G3b: 30–44, G4: 15–29, G5: <15 mL/min/1.73m²), and (3) Albuminuria category (A1: <30, A2: 30–300, A3: >300 mg/g); risk of adverse outcomes (kidney failure, cardiovascular death, mortality) is highest in patients with both lower GFR and higher albuminuria — communicated as heat-map-style risk grid in KDIGO 2012 (still in use as of 2024).
How It's Used on the Ward
"CKD stage 3b" — the standard concise shorthand for chronic kidney disease reported in clinical documentation; "CKD stage 4" triggers nephrology referral and ESRD planning conversations; "CKD G5 on dialysis" — actively receiving renal replacement therapy. Often reported alongside albuminuria ("CKD 3b/A2") for prognosis.
Example
""62-year-old with type 2 diabetes for 18 years, hypertension for 22 years, presents for routine primary care. Most recent labs: eGFR 38 mL/min/1.73m² (down from 42 eighteen months ago), urine albumin/creatinine ratio 220 mg/g. The patient's CKD is staged: G3b (GFR 30-44) and A2 (albuminuria 30-300). KDIGO heat-map: green (low risk) → yellow (moderate) → orange (high). G3bA2 falls in yellow zone — moderate risk of kidney failure or CV event. Plan: optimize BP (target <130/80), maximize SGLT2 inhibitor and ACE/ARB, prepare for nephrology referral if GFR drops below 30 (stage G4). Diabetes control: aim A1c <7.5 in this CKD stage; avoid metformin if eGFR <30.""
Clinical Context
Why KDIGO matters: standardizes communication among nephrologists, primary care, patients; allocates resources (referral, dialysis planning); predicts prognosis and guides medication choices. Albuminuria category: A1 (<30) — normal-to-mildly increased; A2 (30-300) — moderately increased; A3 (>300) — severely increased (formerly called macroalbuminuria or nephrotic-range if >3000). Heat-map risk groups: low risk (G1/G2 with A1; G3a with A1), moderate risk (G3a with A2; G3b with A1), high risk (G3b with A2; G4 with A1), very high risk (G4 with A2/A3; G5 with any). Common medications requiring dose-adjustment by CKD stage: metformin (contraindicated at G5, dose-reduce at G3a-G4), gabapentin/pregabalin (dose-reduce for accumulation), direct oral anticoagulants (renal-dose adjusted), contrast caution. CKD progression: typical rate of decline 1-4 mL/min/year; faster decline in diabetic nephropathy with poor glycemic/BP control; stages advance at non-linear rates. SGLT2 inhibitors (empagliflozin, dapagliflozin) slow CKD progression regardless of diabetes status — now standard of care for CKD with albuminuria. Nephrology referral triggers (KDIGO): G4 (eGFR <30), albuminuria A3 (>300), rapid progression (>5 mL/min/year decline), suspected secondary cause, complex medication management, anemia or metabolic bone disease workup.