Stage 3b Chronic Kidney Disease
A GFR of 34 mL/min/1.73 m² indicates Stage 3b chronic kidney disease, defined as moderately to severely decreased kidney function (GFR 30-44 mL/min/1.73 m²). 1
CKD Staging Classification
The KDIGO classification system defines CKD stages based on eGFR as follows: 1
- Stage G1: ≥90 mL/min/1.73 m²
- Stage G2: 60-89 mL/min/1.73 m²
- Stage G3a: 45-59 mL/min/1.73 m²
- Stage G3b: 30-44 mL/min/1.73 m² (your patient is here)
- Stage G4: 15-29 mL/min/1.73 m²
- Stage G5: <15 mL/min/1.73 m² (kidney failure)
Clinical Significance of Stage 3b
This stage represents loss of approximately two-thirds of normal kidney function and carries substantially increased risks. 1
- Stage 3b is associated with markedly increased cardiovascular disease risk, accelerated CKD progression, and elevated mortality compared to earlier stages 1, 2
- Research demonstrates that perioperative major adverse cardiovascular and cerebrovascular events increase substantially at eGFR <45 mL/min/1.73 m², with odds ratios jumping from 1.8 in stage 3a to 3.9 in stage 3b 3
- Elderly women with CKD stage 3b-5 demonstrate over 3-fold increased risk of death compared to those with stage 1-2 disease 4
Important Diagnostic Considerations
Do not rely on a single eGFR measurement—CKD requires persistent abnormalities for ≥3 months. 1, 2
- Repeat the eGFR within 3 months to confirm chronicity 2
- Never use serum creatinine concentration alone to assess kidney function; always calculate eGFR using validated equations 1
- If the creatinine-based eGFR appears discordant with the clinical picture, measure cystatin C-based eGFR, as creatinine estimates are inaccurate in approximately 16-20% of individuals with eGFR <60 mL/min/1.73 m² 2
Mandatory Actions at This Stage
Nephrology referral is strongly indicated when eGFR <45 mL/min/1.73 m². 2
- Screen for CKD complications every 6-12 months, including blood pressure, volume status, electrolyte abnormalities, metabolic acidosis, anemia, and mineral bone disease 2
- Measure serum calcium and phosphorus every 3-6 months and PTH every 6-12 months in stage 3b 2
- Verify dosing of all medications, as many require adjustment when eGFR <60 mL/min/1.73 m² 2
- Strictly avoid NSAIDs, as they reduce renal blood flow and can precipitate acute kidney injury 2
Common Pitfall
The most critical error is underestimating the severity of stage 3b disease. While stage 3a (eGFR 45-59) and stage 3b (eGFR 30-44) are both labeled "stage 3," the clinical implications differ dramatically—stage 3b carries substantially higher risks for adverse outcomes and requires more aggressive monitoring and nephrology involvement. 1, 3