CKD Staging: KDIGO 2024 Classification & Management Framework
KDIGO 2012 CKD Definition (Still Gold Standard)
Chronic Kidney Disease = kidney damage for ≥3 months manifested by: 1. Albuminuria (any degree) OR 2. GFR <60 mL/min/1.73m² BSA OR 3. Abnormal kidney imaging (cysts, fibrosis, scarring)
CKD is defined by abnormality, not by kidney disease diagnosis. A patient with diabetes WITHOUT albuminuria or low GFR does NOT have CKD.
KDIGO 2024 Staging: G Categories (GFR) + A Categories (Albuminuria)
GFR Categories (G1–G5)
| Category | GFR (mL/min/1.73m²) | Clinical Description |
|---|---|---|
| G1 | ≥90 | Normal or high |
| G2 | 60–89 | Mildly decreased |
| G3a | 45–59 | Mildly-to-moderately decreased |
| G3b | 30–44 | Moderately-to-severely decreased |
| G4 | 15–29 | Severely decreased |
| G5 | <15 | Kidney failure (ESRD) |
Albuminuria Categories (A1–A3)
| Category | UACR (mg/g) | UPCR (g/day) | Clinical Risk |
|---|---|---|---|
| A1 | <30 | <0.5 | Normal to mildly increased |
| A2 | 30–300 | 0.5–3.5 | Moderately increased |
| A3 | >300 | >3.5 | Severely increased (nephrotic) |
UACR conversion: 1 g/day ≈ 1,000 mg/day - Spot UACR >300 mg/g ≈ 24-h proteinuria >3.5 g/day - Nephrotic range proteinuria: >3.5 g/day (or UACR >300)
KDIGO 2024 Heat Map: Risk Stratification
New in 2024: GFR + Albuminuria matrix creates color-coded risk:
A1 (<30) A2 (30-300) A3 (>300)
Green Yellow Orange/Red
G1 (≥90) ✓ Green Yellow Orange
G2 (60-89) ✓ Green Yellow Orange
G3a (45-59) Yellow Yellow Orange
G3b (30-44) Yellow Orange Red
G4 (15-29) Orange Orange Red
G5 (<15) Red Red RedInterpretation: - Green (Low risk): G1–G2 + A1; most don’t need nephrology referral - Yellow (Moderate risk): G3a-G3b ± A1, or G1–G2 + A2; monitor closely - Orange (High risk): G3b–G4 + A2, or any + A3; nephrology referral indicated - Red (Very high risk): G4–G5 ± any A; urgent nephrology
Nephrology referral threshold: - Urgent (same week): G5 (Cr >10 mg/dL), uncontrolled HTN, rapidly declining GFR - Soon (within 2–4 weeks): G3b + albuminuria, G4 ± albuminuria, CKD + diabetes - Routine (within 3 months): G3a + albuminuria, first CKD diagnosis
GFR Estimation: CKD-EPI 2021 Equation
Modern standard: CKD-EPI 2021 (replaces Cockcroft-Gault, MDRD)
Advantages: - Includes cystatin C (more accurate in extremes) - Better at high GFR (overestimation reduced) - Racial demography removed (no longer uses “Black race multiplier”) - More accurate at low GFR
Formula components: - Serum creatinine (Cr) — measured in μmol/L or mg/dL - Cystatin C (optional) — serum cystatin C in mg/L - Age, sex
Online calculator: KDIGO.org (avoids arithmetic errors)
When CKD-EPI differs from MDRD: - CKD-EPI ↑ GFR estimate → LESS overestimation of CKD severity - Pt with Cr 1.2 (MDRD eGFR 60) → CKD-EPI eGFR 65 (not CKD G3 by eGFR alone) - Always use SAME equation for trending; don’t mix calculators
Cystatin C Benefits
- Filtered freely, reabsorbed + catabolized (not reabsorbed like Cr)
- Better marker in: elderly, sarcopenic patients, pregnancy, muscle wasting
- Less affected by diet, muscle mass
Cystatin C GFR equation: CKD-EPI 2012 (or newer 2021 with creatinine)
Risk Factors for CKD Progression & Complications
Non-Modifiable
- Age >60
- Male sex
- Race/ethnicity (African American, Native American, Hispanic — multiple mechanisms, not purely genetic)
- Family history of CKD or ESRD
Modifiable: THE BIG ONES
- Diabetes (most common cause, ~1/3 of ESRD) — tight glucose control (HbA1c <7%), ACE-I/ARB
- Hypertension (2nd most common) — BP target <120 mmHg (SPRINT-CKD concept)
- Albuminuria — reduced by ACE-I/ARB/SGLT2i/finerenone/GLP1-RA
- NSAIDs & other nephrotoxins — avoid with advancing CKD
- Smoking — increases proteinuria, HTN
- Poor diet — sodium ↑, phosphate ↑, potassium ↑
- Obesity — association with progression
Key Management by Stage
CKD G1–G2 with A1 (No referral)
- No kidney disease treatment required if no other indicator
- Regular monitoring: Cr × 1 year, UA × 1 year
- Modify traditional CV risk factors (HTN, lipids, smoking)
CKD G3a (45–59) ± Albuminuria (Routine referral)
- If albuminuria: ACE-I or ARB first-line
- Monitor Cr, K, electrolytes 1–2 weeks after ACE-I start
- Encourage DASH diet, weight loss, exercise
- Target BP: <120 mmHg systolic (SPRINT-CKD)
CKD G3b (30–44) with A2–A3 (Referral within 1 month)
- Triple therapy: ACE-I/ARB + SGLT2i + (finerenone or GLP1-RA if diabetic)
- Monitor bone/mineral (Ca, PO4, PTH, 25-OH VitD)
- Adjust drug dosing (renally cleared meds)
- Prepare for advanced CKD counseling (dialysis, transplant, conservative)
CKD G4 (15–29) (Urgent referral)
- Full nephrology co-management
- Advanced CKD clinic: vascular access creation, transplant eval, dialysis education
- Bone-mineral-disorder (BMD) management: phosphate binders, vitamin D, calcimimetics
- Anemia management: iron, ESA (if Hgb <10 g/dL despite iron)
- Cardiovascular risk reduction
CKD G5 (Cr <15 or already on dialysis) (EMERGENT)
- RRT initiation planning (dialysis start or preemptive transplant)
- Vascular access (fistula, graft)
- Peritoneal access if PD choice
- RRT education before GFR <15 to optimize timing
UACR & 24-Hour Urine Protein Interpretation
When to Order Each
- Spot UACR: Easiest, no 24-h collection needed; preferred for screening
- 24-hour urine: If discordant symptoms (dipstick 2+ but low UACR), large patient, high-protein diet, or research
UACR Thresholds
| UACR (mg/g) | Category | Action |
|---|---|---|
| <30 | Normal/A1 | Reassure; recheck yearly |
| 30–300 | Microalb/A2 | ACE-I/ARB; SGLT2i if DM |
| >300 | Macroalb/A3 | Urgent treatment; consider nephrotic workup if >1 g/day |
False high UACR: Fever, UTI, menstruation, intense exercise, hypertension crisis False low UACR: Dilute urine (high urine volume) Repeat if markedly abnormal and clinically discordant.
CKD-MBD (Mineral-Bone Disorder): Screening by Stage
Start mineral screening at G3a; more frequent at G3b–G5:
| Test | G1–G3a | G3b | G4 | G5 |
|---|---|---|---|---|
| Serum Ca, PO4 | Yearly | Yearly | Q6 months | Monthly–Q6 weeks |
| PTH | Once if G3a | Q12 months | Q3–6 months | Q3 months |
| 25-OH Vitamin D | Once | Once | Once | Q6–12 months |
| FGF23 | Rarely | If progression rapid | If progression rapid | Not routine |
Screening findings: - PTH >100 pg/mL at GFR 45–59 → Start vitamin D - PO4 >4.5 mg/dL → Diet counseling + consider binders at G4 - Ca-PO4 product >55 → Risk of vascular calcification
Referral Criteria Summary (Handy Chart)
| Indication | Timing |
|---|---|
| CKD diagnosis (new) | Routine |
| G3b + albuminuria | Within 1 month |
| G4 ± albuminuria | Within 2 weeks |
| G5 (ESRD) | URGENT same day |
| Rapidly declining GFR (>5 mL/min/year drop) | Urgent |
| Uncontrolled HTN despite 3+ drugs | Urgent |
| Protein >3.5 g/day (nephrotic) | Urgent |
| Abnormal kidney imaging | Within 1 month |
Self-Test Questions
- 72M, Cr 1.5 (baseline 1.2), no albuminuria, BP 140/85 on HCTZ
- GFR estimate (CKD-EPI): ~48 mL/min (G3b)
- Albuminuria category: A1
- Risk: Moderate-yellow (G3b + A1)
- Action: ACE-I/ARB start, BP target <120
- 45F with DM, Cr 0.9, UACR 250 mg/g, BP 125/80 on lisinopril
- GFR: ~70 (G2)
- Albuminuria: A2
- Risk: Moderate-yellow (G2 + A2)
- Action: Add SGLT2i, target HbA1c <7%, routine referral
- 68M, Cr 2.8, K 5.8, PO4 5.2, PTH 180
- GFR: ~20 (G4)
- Risk: Red (G4 + any A)
- Action: Urgent nephrology, start BMD management, plan RRT
Version 1.0 | PA/Medical student level | Updated 2026-02-28
References: KDIGO 2024 Clinical Practice Guideline for the Management of CKD. Am J Kidney Dis. 2024 (newest). CKD-EPI Collaboration. A new equation to estimate glomerular filtration rate. Ann Intern Med. 2009;150(9).