Specialty Spotlights
Nephrology Calculators Spotlight: eGFR, FENa, UACR, and AKI Staging
Kidney disease touches every specialty. This spotlight covers five essential nephrology calculators: CKD-EPI eGFR (chronic function), FENa (AKI differentiation), urine albumin-creatinine ratio (early injury/proteinuria), KDIGO AKI staging (acute severity), and Cockcroft-Gault (drug dosing). Know when to use each — and when not to.
TL;DR: Kidney disease touches every specialty. This spotlight covers five essential nephrology calculators: CKD-EPI eGFR (chronic function), FENa (AKI differentiation), UACR (early injury/proteinuria), KDIGO AKI staging (acute severity), and Cockcroft-Gault (drug dosing).
Calculator 1: CKD-EPI eGFR (2021)
Estimates GFR from serum creatinine, age, and sex. Used for CKD staging.
| G-Stage | eGFR | Clinical Stage |
|---|---|---|
| G1 | ≥90 | Normal/high |
| G2 | 60–89 | Mildly decreased |
| G3a | 45–59 | Mildly-moderately decreased |
| G3b | 30–44 | Moderately-severely decreased |
| G4 | 15–29 | Severely decreased |
| G5 | <15 | Kidney failure |
Calculator 2: Cockcroft-Gault CrCl
CrCl = [(140 − Age) × Weight] / [72 × Serum Cr] × (0.85 if Female)
Used for drug dosing — not CKD staging.
Calculator 3: UACR
| Category | UACR (mg/g) | Description |
|---|---|---|
| A1 | <30 | Normal |
| A2 | 30–300 | Moderately increased |
| A3 | >300 | Severely increased |
Earliest marker of glomerular injury. Annual screening for all diabetics and hypertensives.
Calculator 4: KDIGO AKI Staging
| Stage | Creatinine Criteria | UO Criteria |
|---|---|---|
| 1 | ≥0.3 mg/dL rise OR 1.5–1.9× baseline | <0.5 mL/kg/hr for 6–12 hr |
| 2 | 2.0–2.9× baseline | <0.5 mL/kg/hr for ≥12 hr |
| 3 | ≥3× baseline OR ≥4.0 OR RRT | <0.3 mL/kg/hr for ≥24 hr OR anuria ≥12 hr |
Calculator 5: FENa and FEUrea
| Biomarker | Prerenal | Intrinsic |
|---|---|---|
| FENa | <1% | ≥1% |
| FEUrea | <35% | ≥35% |
| Urine Na | <20 | >40 |
Evidence Summary
Abdelhafez M et al. (2022): FENa Se 95%, Sp 91% in oliguric patients without CKD/diuretics. CJASN. 2022;17(6):785–797. PMID: 35545442.
Delanaye P et al. (2023): CKD-EPI 2021 remains the global standard; EKFC equation may be better in young adults and diverse European populations. Clin Kidney J. 2023;16(9):1375–1383. PMID: 37664574.
References
- Abdelhafez M et al. CJASN. 2022;17(6):785–797. PMID: 35545442.
- Delanaye P et al. Clin Kidney J. 2023;16(9):1375–1383. PMID: 37664574.
- KDIGO AKI Work Group. Kidney Int Suppl. 2012;2(1):1–138.
- KDIGO CKD Work Group. Kidney Int Suppl. 2024.
- Levey AS et al. Ann Intern Med. 2009;150(9):604–612. PMID: 19414839.