## KDIGO CKD Staging by GFR **Key Point:** CKD Stage 4 is defined by severely reduced GFR of 15–29 mL/min/1.73 m². At this stage, patients require preparation for renal replacement therapy and close monitoring for complications [cite:KDIGO 2012]. ### CKD Stages and GFR Classification | Stage | GFR (mL/min/1.73 m²) | Clinical Significance | | --- | --- | --- | | **1** | ≥90 | Normal or high; kidney damage present | | **2** | 60–89 | Mildly decreased | | **3a** | 45–59 | Mildly to moderately decreased | | **3b** | 30–44 | Moderately to severely decreased | | **4** | 15–29 | **Severely decreased** | | **5** | <15 | Kidney failure; requires RRT | **High-Yield:** Stage 4 CKD is the critical threshold where: - Referral to nephrology is urgent (if not already done). - Preparation for dialysis or transplant begins. - Mineral-bone disorder (CKD-MBD) becomes clinically significant. - Cardiovascular complications accelerate. - Anemia and malnutrition require active management. **Mnemonic:** **GFRS** — GFR ≥90 (Stage 1), 60–89 (Stage 2), 45–59 (Stage 3a), 30–44 (Stage 3b), 15–29 (Stage **4**), <15 (Stage 5). **Clinical Pearl:** A patient with GFR 20 mL/min/1.73 m² is in Stage 4 and typically requires: - Nephrology follow-up every 1–3 months. - Vascular access planning (fistula creation or catheter insertion). - Dietary counseling (protein, phosphorus, potassium restriction). - Blood pressure control and cardiovascular risk reduction. 
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