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For educational purposes only. Not a substitute for clinical judgment.
CKD Staging by eGFR
| Stage | eGFR (mL/min/1.73m²) | Description |
|---|---|---|
| G1 | ≥ 90 | Normal or high kidney function |
| G2 | 60–89 | Mildly decreased |
| G3a | 45–59 | Mildly to moderately decreased |
| G3b | 30–44 | Moderately to severely decreased |
| G4 | 15–29 | Severely decreased — prepare for RRT |
| G5 | < 15 | Kidney failure (dialysis or transplant needed) |
The CKD-EPI 2021 Equation (Race-Free)
The 2021 CKD-EPI equation uses only serum creatinine, age, and sex. For females: eGFR = 142 × min(Scr/0.7, 1)^−0.241 × max(Scr/0.7, 1)^−1.200 × 0.9938^Age × 1.012. For males: replace 0.7 with 0.9, −0.241 with −0.302, and remove the 1.012 sex multiplier. The 2009 equation included a race coefficient that increased estimated GFR in Black patients — a correction that was later found to delay nephrology referrals and dialysis initiation. The 2021 race-free formula eliminates this disparity and is now the recommended standard.
High-Yield Points for USMLE / NCLEX
Key testable facts: (1) eGFR < 60 for > 3 months = CKD by definition (regardless of cause or symptoms); (2) normal serum creatinine does not exclude reduced GFR — creatinine rises above normal only after ~50% of nephron loss; (3) cystatin C-based GFR is more accurate in patients with abnormal muscle mass (amputees, bodybuilders); (4) contrast nephropathy risk increases significantly at eGFR < 30; (5) metformin is contraindicated at eGFR < 30 (hold if < 45 before contrast); (6) dose-adjust renally-cleared drugs (aminoglycosides, vancomycin, digoxin) using eGFR.
When to Refer to Nephrology
KDIGO guidelines recommend nephrology referral for: eGFR < 30 (G4/G5), rapidly declining eGFR (> 5 mL/min/yr or > 25% decline in < 12 months), eGFR < 60 with other complications (uncontrolled hypertension, anemia, CKD-MBD), nephrotic-range proteinuria (> 3.5g/24h or urine PCR > 3500 mg/g), or when the cause of CKD is unclear. Timely nephrology referral is associated with better vascular access planning and improved ESRD outcomes.
Frequently Asked Questions
What eGFR is normal for age 70?
eGFR naturally declines with age — approximately 1 mL/min/1.73m² per year after age 40. A 70-year-old with an eGFR of 60–75 may have normal age-related decline rather than true CKD. KDIGO notes that many older adults with eGFR 45–59 without albuminuria or other markers of kidney damage may not have 'true' CKD — this is an area of ongoing debate. In practice, CKD is still diagnosed based on the < 60 threshold regardless of age, but the clinical significance at eGFR 50–60 in an 80-year-old is very different from a 40-year-old.
How accurate is the CKD-EPI equation?
The CKD-EPI 2021 equation has a bias of ±5–10% compared to measured GFR (via iothalamate or inulin clearance) in most patients. It is least accurate in: (1) extremes of muscle mass (bodybuilders, amputees, malnutrition); (2) acute kidney injury (creatinine is not at steady state); (3) vegetarian diets (lower baseline creatinine from dietary sources may overestimate GFR). In these situations, cystatin C-based equations (eGFR_CysC) provide better estimates.
What is the difference between eGFR and creatinine clearance?
Creatinine clearance (CrCl, calculated via Cockcroft-Gault) estimates actual clearance in mL/min and is preferred for drug dosing calculations because most drug pharmacokinetic studies were conducted using CrCl. eGFR (CKD-EPI) is normalized to body surface area (mL/min/1.73m²) and is preferred for staging CKD. In practical terms: use CrCl for drug dosing, use eGFR for CKD staging and disease monitoring. They often yield similar values but can diverge significantly in patients with unusual body habitus.
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