About This eGFR Calculator
This dual-mode renal function calculator computes both the CKD-EPI 2021 eGFR and the Cockcroft-Gault creatinine clearance (CrCl) from a single set of inputs. In radiology, both values appear in clinical workflows: eGFR drives contrast safety decisions (ACR guidelines), while Cockcroft-Gault CrCl appears in many EMRs and drug dosing references.
CKD-EPI 2021 Formula
eGFR = 142 × min(Scr/κ, 1)α × max(Scr/κ, 1)−1.200 × 0.9938Age × (1.012 if Female)
Where κ = 0.7 (female) or 0.9 (male), α = −0.241 (female) or −0.302 (male). The 2021 revision removed the race coefficient, addressing racial health equity concerns while preserving accuracy across populations. It is endorsed by KDIGO, NKF, and ASN.
Cockcroft-Gault Formula
CrCl = [(140 − Age) × Weight(kg) / (72 × Scr(mg/dL))] × 0.85 if Female
This formula was derived in 1976 from 249 hospitalized men. Despite its age, most drug labeling still specifies CrCl — not eGFR — as the dosing metric. For obese patients (actual body weight > ideal body weight), use adjusted body weight (ABW = IBW + 0.4 × [actual − IBW]) to avoid overestimation of CrCl. This calculator shows both unadjusted and IBW-adjusted values when height is provided.
CKD Stage Classification (KDIGO 2022)
| Stage | eGFR (mL/min/1.73m²) | Description | Iodinated Contrast | Metformin |
|---|---|---|---|---|
| G1 | ≥ 90 | Normal or high | Safe, standard precautions | Continue |
| G2 | 60–89 | Mildly decreased | Safe, standard precautions | Continue |
| G3a | 45–59 | Mild-moderate decrease | Proceed; hydration recommended | Hold 48h post-contrast if eGFR < 45 |
| G3b | 30–44 | Moderate-severe decrease | Proceed with IV hydration; nephrology input | Hold at time of contrast; restart after 48h if stable |
| G4 | 15–29 | Severely decreased | Risk-benefit discussion; minimize volume | Hold; nephrology co-management |
| G5 | < 15 (or dialysis) | Kidney failure | Avoid unless clinical benefit outweighs risk; dialysis pts may receive | Contraindicated at this stage |
Gadolinium-Based Contrast Agents (GBCA) and NSF
Nephrogenic systemic fibrosis (NSF) is a rare but serious complication of high-dose linear ionic gadolinium agents in severe renal impairment. The ACR currently recommends:
- eGFR ≥ 30: All FDA-approved GBCAs can be administered at standard doses. No NSF cases have been confirmed with macrocyclic agents at any eGFR level.
- eGFR 15–29: Prefer macrocyclic agents (gadobutrol, gadoteridol, gadoterate meglumine). Avoid high-dose protocols. Discuss with ordering physician.
- eGFR < 15 or dialysis: Macrocyclic agents may be used when clearly indicated. Avoid linear ionic GBCAs entirely. Schedule hemodialysis promptly after administration if possible.
Metformin and Iodinated Contrast — ACR 2024
The ACR 2024 guidance simplifies metformin management:
- eGFR ≥ 30, no AKI: Continue metformin. Reassess renal function 48 hours post-contrast before continuing if large volume contrast was given.
- eGFR < 30, or AKI present: Hold metformin at the time of contrast and for 48 hours. Recheck eGFR before restarting.
- Rationale: IV contrast does not directly interact with metformin. The concern is that CI-AKI reduces metformin clearance, which may cause metformin-associated lactic acidosis (MALA) in rare cases.
CKD-EPI vs Cockcroft-Gault — When to Use Each
Despite being measured from the same serum creatinine, these equations give different results because they model different things:
| Feature | CKD-EPI 2021 | Cockcroft-Gault |
|---|---|---|
| What it estimates | GFR normalized to 1.73m² BSA | Creatinine clearance (absolute, unadjusted) |
| Race correction | None (2021 update) | None |
| Weight variable | Not used | Required |
| Best used for | CKD staging, contrast decisions | Drug dosing (DOAC, antibiotics, chemotherapy) |
| Reference body | 1.73m² BSA standardized | Actual/adjusted body weight |
| Guideline endorsement | KDIGO, NKF, ACR | FDA drug labels, many pharmacokinetic studies |
Limitations
Both equations are less accurate in: pediatric patients (use Schwartz equation), patients with extremes of muscle mass (amputees, bodybuilders, cachexia), vegetarians/vegans (lower creatinine production), and acute kidney injury (use creatinine trends, not eGFR). When in doubt, cystatin C-based eGFR (CKD-EPI 2021 cystatin C) provides a complementary estimate not dependent on muscle mass.
References
Inker LA, et al. New Creatinine- and Cystatin C–Based Equations to Estimate GFR without Race. N Engl J Med. 2021;385:1737–1749.
Cockcroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine. Nephron. 1976;16(1):31–41.
KDIGO 2022 CKD Guideline. Kidney Int Suppl. 2022;104(4S):S117–S314.
ACR Manual on Contrast Media. American College of Radiology, 2023 edition.