40 year male serum creatinine 1.29 mg/dl serum cystatin c 1.13mg / L calculate EGFR
Reading File
I'll calculate the eGFR using the standard CKD-EPI equations directly. This is a well-established calculation that I can perform now.
eGFR Calculation
Patient: 40-year-old male
Serum Creatinine: 1.29 mg/dL
Serum Cystatin C: 1.13 mg/L
1. CKD-EPI Creatinine 2021 (race-free)
Formula for males:
eGFR = 142 × (Scr/κ)^α × (0.9938)^Age
Where for males: κ = 0.9, α = −0.302 (if Scr ≤ 0.9), or α = −1.200 (if Scr > 0.9)
Since 1.29 > 0.9:
- Scr/κ = 1.29/0.9 = 1.4333
- (1.4333)^−1.200 = e^(−1.200 × ln(1.4333)) = e^(−1.200 × 0.3596) = e^(−0.4315) = 0.6497
- (0.9938)^40 = e^(40 × ln(0.9938)) = e^(40 × −0.006219) = e^(−0.2488) = 0.7797
eGFR (Cr) = 142 × 0.6497 × 0.7797 = 71.9 mL/min/1.73 m²
2. CKD-EPI Cystatin C 2012
Formula:
eGFR = 133 × (CysC/0.8)^α × (0.9961)^Age [× 0.932 if female]
Where for CysC ≤ 0.8: α = −0.499; for CysC > 0.8: α = −1.328
Since 1.13 > 0.8:
- CysC/0.8 = 1.13/0.8 = 1.4125
- (1.4125)^−1.328 = e^(−1.328 × ln(1.4125)) = e^(−1.328 × 0.3452) = e^(−0.4584) = 0.6324
- (0.9961)^40 = e^(40 × −0.003908) = e^(−0.1563) = 0.8554
eGFR (CysC) = 133 × 0.6324 × 0.8554 = 71.9 mL/min/1.73 m²
3. CKD-EPI Creatinine-Cystatin C Combined 2021 (most accurate)
Formula for males with Scr > 0.9 and CysC > 0.8:
eGFR = 135 × (Scr/0.9)^−0.544 × (CysC/0.8)^−0.323 × (0.9961)^Age
- (1.29/0.9)^−0.544 = (1.4333)^−0.544 = e^(−0.544 × 0.3596) = e^(−0.1956) = 0.8224
- (1.13/0.8)^−0.323 = (1.4125)^−0.323 = e^(−0.323 × 0.3452) = e^(−0.1115) = 0.8944
- (0.9961)^40 = 0.8554
eGFR (Cr+CysC) = 135 × 0.8224 × 0.8944 × 0.8554 = 84.9 mL/min/1.73 m²
Summary Table
| Equation | eGFR (mL/min/1.73 m²) | CKD Stage |
|---|---|---|
| CKD-EPI Creatinine 2021 | ~72 | G2 (mildly decreased) |
| CKD-EPI Cystatin C 2012 | ~72 | G2 (mildly decreased) |
| CKD-EPI Cr+CysC Combined 2021 | ~85 | G1 (normal/high) |
Clinical Interpretation
- The combined Cr+CysC equation is the most accurate when both markers are available and is the preferred equation per KDIGO 2024 guidelines.
- The combined eGFR of ~85 mL/min/1.73 m² places this patient in CKD Stage G1 (≥ 90 is normal; 60–89 is G2).
- The concordance between the creatinine-only and cystatin-only results (~72 each) suggests no significant non-GFR determinant bias (e.g., from muscle mass or steroid use).
- A single eGFR value is insufficient to diagnose CKD — structural abnormalities or repeat eGFR < 60 persisting > 3 months is required for CKD diagnosis per KDIGO.
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