Five validated GFR equations and four clinical tools in one place — from CKD-EPI 2021 eGFR to the KDIGO risk map, kidney-failure risk, drug-dosing weights and MRI contrast safety. Range-checked inputs, instant staging, copy-ready summaries.
Estimates GFR using the 2021 race-free CKD-EPI creatinine equation — the current standard for CKD staging and monitoring. Not valid in AKI or pregnancy.
| Stage | eGFR (mL/min/1.73 m²) | Description |
|---|---|---|
| G1 | ≥ 90 | Normal or high kidney function |
| G2 | 60–89 | Mildly decreased |
| G3a | 45–59 | Mild to moderately decreased |
| G3b | 30–44 | Moderately to severely decreased |
| G4 | 15–29 | Severely decreased |
| G5 | < 15 | Kidney failure |
| AKI | Not valid — requires stable SCr ≥ 3 months |
| Pregnancy | Not validated in pregnant patients |
| Paediatric (<18 yr) | Not validated |
| Transplant recipients | Not validated |
| Extreme muscle mass | Reduced accuracy (sarcopenia, amputees, bodybuilders) |
| Creatinine assay | Must be IDMS-standardised measurement |
Inker LA, Eneanya ND, Coresh J, et al. New Creatinine- and Cystatin C–Based Equations to Estimate GFR without Race. N Engl J Med. 2021;385(19):1737–1749. PMID: 34554658
Estimates creatinine clearance (CrCl) using age, weight, sex, and serum creatinine. The established standard for medication dose adjustment in renal impairment — used by almost all drug package inserts.
| Category | CrCl (mL/min) | Drug Dosing Implication |
|---|---|---|
| Normal | ≥ 90 | Standard dosing for most renally-cleared drugs |
| Mild impairment | 60–89 | Monitor; minor adjustments for select drugs |
| Moderate impairment | 30–59 | Dose reduction required for many drugs |
| Severe impairment | 15–29 | Significant reductions; specialist review recommended |
| Kidney failure | < 15 | Many drugs contraindicated; dialysis-specific protocols |
| Not eGFR | CrCl ≠ eGFR — not used for CKD staging; for drug dosing only |
| Obesity | ABW overestimates; use IBW or AdjBW per drug monograph |
| Elderly / sarcopenic | Low muscle mass → low SCr → CrCl overestimated |
| AKI | Not valid in acute kidney injury |
| Tubular secretion | CrCl overestimates true GFR by ~10–20% (creatinine is secreted) |
Cockcroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine. Nephron. 1976;16(1):31–41. PMID: 1244564
Estimates GFR using serum cystatin C — less influenced by muscle mass, diet, and body composition than creatinine. Preferred when creatinine-based estimates may be unreliable.
| Sarcopenia / amputees | Low muscle mass makes creatinine unreliable; cystatin C is unaffected |
| Malnourishment | Creatinine underestimates impairment; cystatin C more reliable |
| Elderly patients | Age-related muscle loss distorts creatinine-based estimates |
| Vegetarians / vegans | Low dietary creatine reduces creatinine, biasing CKD-EPI eGFR high |
| Confirmatory (G3a) | KDIGO suggests cystatin C to confirm CKD when eGFRcr is 45–59 without other markers of damage. For the best estimate use the combined Cr–Cys equation |
| Bodybuilders | High muscle mass elevates creatinine, masking true impairment |
| Thyroid disease | Hypothyroidism raises, hyperthyroidism lowers cystatin C independent of GFR |
| Corticosteroids | Increase cystatin C production; may overestimate renal impairment |
| Malignancy | Some tumours alter cystatin C levels non-renally |
| AKI | Not validated in acute kidney injury |
| Paediatric | Not validated in patients under 18 years |
| Assay cost | Cystatin C is more expensive than creatinine; not universally available |
Inker LA, Schmid CH, Tighiouart H, et al. Estimating glomerular filtration rate from serum creatinine and cystatin C. N Engl J Med. 2012;367(1):20–29. DOI: 10.1056/NEJMoa1114248 · PMID: 22762315
Combines serum creatinine and cystatin C — the most accurate eGFR equation. KDIGO 2024 recommends it when a confirmatory estimate is needed.
Stages CKD by eGFR (G1–G5) and albuminuria (A1–A3) and places the patient on the KDIGO prognosis heat map.
CKD is defined by eGFR < 60 mL/min/1.73 m² and/or markers of kidney damage (such as albuminuria ACR ≥ 30 mg/g) present for more than 3 months. The colour combines both measures: green low risk, yellow moderately increased, orange high and red very high risk of adverse outcomes.
ACR conversion: 1 mg/mmol = 8.84 mg/g. A1 < 3 mg/mmol, A2 3–30 mg/mmol, A3 > 30 mg/mmol.
Predicts the 2- and 5-year risk of kidney failure needing dialysis or transplant in adults with CKD G3–G5.
Works out ideal and adjusted body weight, BMI and BSA, then gives Cockcroft-Gault CrCl for each weight and the de-indexed eGFR (mL/min) used by some drug labels.
Weight choice rules vary between drugs and institutions. Always follow the specific drug monograph.
Reference summary of renal precautions for gadolinium-based contrast agents, by ACR agent group, eGFR, dialysis and AKI status.
| Group | Agents | NSF risk |
|---|---|---|
| Group I | Gadodiamide, gadopentetate dimeglumine, gadoversetamide | Highest — avoid with eGFR < 30, dialysis or AKI |
| Group II | Gadobenate dimeglumine, gadobutrol, gadoterate meglumine, gadoteridol, gadoxetate disodium | Very low — renal screening optional |
This page summarises published guidance for reference. It does not replace your department's contrast policy or a radiologist's judgement.
The Modification of Diet in Renal Disease (MDRD) 4-variable equation. Largely superseded by CKD-EPI 2021 — notably underestimates GFR when eGFR > 60. Still reported by some labs for historical continuity.
| Feature | MDRD (1999) | CKD-EPI 2021 |
|---|---|---|
| Published | 1999 (IDMS 2007) | 2021 |
| Race coefficient | Yes (deprecated) | No |
| Accuracy eGFR > 60 | Underestimates | More accurate |
| Accuracy eGFR < 60 | Comparable | More accurate |
| Recommended for staging | No (replaced) | Yes — current standard |
| Variables used | SCr, age, sex (race) | SCr, age, sex |
Levey AS, Bosch JP, Lewis JB, et al. A more accurate method to estimate glomerular filtration rate from serum creatinine. Ann Intern Med. 1999;130(6):461–470. PMID: 10075613
Levey AS, Coresh J, Greene T, et al. Expressing the MDRD equation for estimating GFR with standardized serum creatinine values. Clin Chem. 2007;53(4):766–772. PMID: 17332152
Calculate all four renal function equations from a single set of inputs and compare results side by side. Cystatin C is optional — leave blank to skip that calculation.
What each tool does, when to use it, what it needs and how to read the result.
SpinCalc brings together five GFR equations and four clinical tools. Calculations run on the MRISpin server; no patient data is stored or logged.
Pick a tool from the sidebar (on a phone, the Menu tab), or press Ctrl K / ⌘ K to search. Each tool has a Clear button. Results can be copied as a plain-text summary or printed as a one-page report. Every tool has its own link (for example spincalc.mrispin.com/#kfre) for bookmarking.
Inputs are range-checked before calculation. If a value is outside the accepted range, the field turns red and a message explains the valid range.
What it is: The race-free 2021 CKD-EPI creatinine equation (Inker 2021), recommended by the NKF-ASN Task Force and KDIGO 2024 as the default for adults.
Use it for: CKD staging and monitoring. This is the equation most laboratories now report.
Inputs: Biological sex, age (18–120 y), IDMS-standardised serum creatinine in mg/dL (0.2–20) or µmol/L (18–1768).
Reading the result: The value maps to G1–G5. CKD needs abnormal results for more than 3 months, and albuminuria (use the KDIGO Risk Map) for full staging.
Not valid in: Acute kidney injury or unstable creatinine, pregnancy, under 18, and extremes of muscle mass (amputation, bodybuilders, sarcopenia).
What it is: The combined 2021 equation using both markers. It is more accurate than either marker alone because their non-GFR errors partly cancel.
Use it for: Confirming CKD (for example eGFRcr 45–59 with no other damage markers), and decisions where accuracy matters: drug dosing near a threshold, kidney donation, chemotherapy.
Inputs: Sex, age, serum creatinine and IFCC-standardised cystatin C (0.3–8 mg/L).
Reading the result: SpinCalc also shows eGFRcr and eGFRcys. A difference of 30% or more flags a likely non-GFR influence on one marker; the combined value is then the most reliable.
What it is: Creatinine clearance (1976), not GFR. Many drug labels define renal dose thresholds with it.
Use it for: Renal drug dosing. Not for CKD staging.
Inputs: Sex (female × 0.85), age, body weight in kg or lbs, serum creatinine.
Weight: Use the Drug Dosing Kit to compare CrCl with actual, ideal and adjusted weight. Always follow the drug monograph.
What it is: The cystatin C-only equation from Inker 2012. It never included a race term, so it remains the recommended cystatin C equation.
Use it for: When creatinine is unreliable: low muscle mass, malnutrition, amputation, vegetarian diet, very high muscle mass.
Inputs: Sex (female × 0.932), age (0.996age) and IFCC-standardised cystatin C in mg/L.
Confounders: Thyroid disease, corticosteroids, inflammation and some cancers change cystatin C independently of GFR.
What it is: The IDMS-traceable MDRD equation (175 × SCr−1.154 × age−0.203), without the race coefficient.
Use it for: Reconciling with older reports only. It underestimates GFR above 60 mL/min/1.73 m².
What it does: Combines the G category (eGFR) and A category (urine albumin-to-creatinine ratio) and highlights the patient's cell on the KDIGO prognosis heat map: green low, yellow moderately increased, orange high, red very high risk.
Inputs: Urine ACR in mg/g or mg/mmol (1 mg/mmol = 8.84 mg/g). Then either type an eGFR, or leave it blank and enter age, sex and creatinine so CKD-EPI 2021 is used.
Thresholds: A1 < 30 mg/g (< 3 mg/mmol), A2 30–300 mg/g (3–30 mg/mmol), A3 > 300 mg/g (> 30 mg/mmol).
Reading the result: Green in G1–G2 means no CKD unless other markers of kidney damage exist. The colour guides monitoring frequency and referral.
What it does: The 4-variable Kidney Failure Risk Equation (Tangri 2011, recalibrated 2016) predicts the chance of needing dialysis or a transplant within 2 and 5 years.
Inputs: Age, sex, eGFR (typed or calculated) and urine ACR. Choose the non-North American calibration for UK, Europe, Middle East and Asia, or the North American calibration for the US and Canada.
Validity: Validated for eGFR 10–59 mL/min/1.73 m² (CKD G3–G5). A warning appears outside this range.
Thresholds shown: 5-year risk > 5%: NICE NG203 nephrology referral threshold. KDIGO 2024 suggests referral at 3–5% five-year risk, and preparation for kidney replacement therapy at 2-year risk ≥ 40%.
What it does: From height, weight, age, sex and creatinine it gives ideal body weight (Devine), adjusted body weight (IBW + 0.4 × excess), BMI, BSA (Mosteller), Cockcroft-Gault CrCl for each weight, and eGFR de-indexed to the patient's BSA (mL/min).
Suggested weight: Actual weight if below IBW; IBW if actual weight is 100–130% of IBW; adjusted weight if above 130%. This is a common convention — many drugs specify their own rule.
De-indexed eGFR: eGFR × BSA / 1.73. Some labels (for example DOACs, some antivirals) use absolute GFR in mL/min, which matters most at extremes of body size.
What it does: Summarises ACR guidance on nephrogenic systemic fibrosis (NSF) risk for the selected gadolinium agent, using eGFR, dialysis and AKI status.
Agent groups: Group I (gadodiamide, gadopentetate dimeglumine, gadoversetamide): avoid with eGFR < 30, dialysis or AKI. Group II (gadobenate, gadobutrol, gadoterate, gadoteridol, and gadoxetate since the 2024 ACR Manual): very low risk; screening optional.
Key point: The 2021 ACR–NKF consensus states that for group II agents the risk of withholding a clinically indicated examination likely outweighs the risk of NSF, even with eGFR < 30.
Limits: A reference summary only. It does not replace your department's contrast policy or radiologist judgement.
Runs every equation from one set of inputs. Weight adds Cockcroft-Gault CrCl; cystatin C adds both the cystatin C-only and the combined Cr–Cys estimate. Missing optional inputs show as "not calculated".
Differences between equations are expected: CKD-EPI 2021 is the reference creatinine equation, MDRD runs lower above 60, CrCl runs higher because creatinine is also secreted by the tubules, and the cystatin C estimates diverge when muscle mass affects creatinine.
The primary papers and guidelines behind every equation and tool in SpinCalc.
Inker LA, Eneanya ND, Coresh J, et al. New creatinine- and cystatin C–based equations to estimate GFR without race. N Engl J Med. 2021;385(19):1737–1749.
DOI: 10.1056/NEJMoa2102953 · PMID: 34554658
Inker LA, Schmid CH, Tighiouart H, et al. Estimating glomerular filtration rate from serum creatinine and cystatin C. N Engl J Med. 2012;367(1):20–29.
DOI: 10.1056/NEJMoa1114248 · PMID: 22762315
Cockcroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine. Nephron. 1976;16(1):31–41.
DOI: 10.1159/000180580 · PMID: 1244564
Levey AS, Bosch JP, Lewis JB, et al. A more accurate method to estimate glomerular filtration rate from serum creatinine: a new prediction equation. Ann Intern Med. 1999;130(6):461–470.
DOI: 10.7326/0003-4819-130-6-199903160-00002 · PMID: 10075613
Levey AS, Coresh J, Greene T, et al. Expressing the Modification of Diet in Renal Disease Study equation for estimating glomerular filtration rate with standardized serum creatinine values. Clin Chem. 2007;53(4):766–772.
DOI: 10.1373/clinchem.2006.078287 · PMID: 17332152
Tangri N, Stevens LA, Griffith J, et al. A predictive model for progression of chronic kidney disease to kidney failure. JAMA. 2011;305(15):1553–1559.
Tangri N, Grams ME, Levey AS, et al. Multinational assessment of accuracy of equations for predicting risk of kidney failure: a meta-analysis. JAMA. 2016;315(2):164–174.
DOI: 10.1001/jama.2015.18202 · PMC: PMC4752167
Weinreb JC, Rodby RA, Yee J, et al. Use of intravenous gadolinium-based contrast media in patients with kidney disease: consensus statements from the American College of Radiology and the National Kidney Foundation. Radiology. 2021;298(1):28–35.
DOI: 10.1148/radiol.2020202903 · PMID: 33170103
ACR Committee on Drugs and Contrast Media. ACR Manual on Contrast Media. American College of Radiology, 2024 edition (group classification of GBCAs, including gadoxetate as group II).
Devine BJ. Gentamicin therapy. Drug Intell Clin Pharm. 1974;8:650–655.
Mosteller RD. Simplified calculation of body-surface area. N Engl J Med. 1987;317(17):1098.
KDIGO CKD Work Group. KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int. 2024;105(4S):S117–S314.
DOI: 10.1016/j.kint.2023.10.018 · PMID: 38490803 · kdigo.org
Delgado C, Baweja M, Crews DC, et al. A unifying approach for GFR estimation: recommendations of the NKF-ASN Task Force on reassessing the inclusion of race in diagnosing kidney disease. Am J Kidney Dis. 2022;79(2):268–288.
DOI: 10.1053/j.ajkd.2021.08.003 · PMID: 34563581
National Institute for Health and Care Excellence. Chronic kidney disease: assessment and management. NICE guideline NG203, 2021 (updated). Includes the 5-year KFRE > 5% referral criterion.
Creatinine: 1 mg/dL = 88.4 µmol/L — derived from the molar mass of creatinine (113.12 g/mol): 10 dL/L ÷ 113.12 g/mol × 1000. Albuminuria: 1 mg/mmol = 8.84 mg/g (the same factor, since ACR is divided by creatinine). Height: 1 in = 2.54 cm. Weight: 1 lb = 0.4536 kg.
Myers GL, Miller WG, Coresh J, et al. Recommendations for improving serum creatinine measurement: a report from the Laboratory Working Group of the National Kidney Disease Education Program. Clin Chem. 2006;52(1):5–18.
Grubb A, Blirup-Jensen S, Lindström V, et al. First certified reference material for cystatin C in human serum ERM-DA471/IFCC. Clin Chem Lab Med. 2010;48(11):1619–1621.
Questions, bug reports or feedback about SpinCalc — get in touch with the MRISpin team.
- New calculator: CKD-EPI 2021 creatinine–cystatin C, with eGFRcr / eGFRcys discordance check.
- New clinical tools: KDIGO Risk Map, Kidney Failure Risk (KFRE), Drug Dosing Kit and MRI Contrast Check.
- Copy summary and Print report on every new tool.
- Accuracy fixes: the female factor (× 1.012) in CKD-EPI 2021 and the age term (0.996) in the cystatin C equation now match the published equations exactly.
- Compare All now includes the combined Cr–Cys estimate when cystatin C is entered.
- Clearer range messages, corrected references and refreshed documentation.
Is patient data stored or sent anywhere?
Inputs are sent over HTTPS to the MRISpin server, calculated, and only the result is returned. Nothing is stored, logged or retained.
Which equation should I use for CKD staging?
CKD-EPI 2021 (creatinine), with the urine ACR on the KDIGO Risk Map. When you need confirmation, use the combined Cr–Cys equation.
Which should I use for drug dosing?
Whichever the drug label specifies. Most labels use Cockcroft-Gault CrCl; some use eGFR in mL/min. The Drug Dosing Kit shows both, for each body weight.
When should I use the KFRE?
For adults with CKD G3–G5 (eGFR 10–59). A 5-year risk above 5% meets the NICE referral criterion; a 2-year risk of 40% or more is the KDIGO threshold to plan kidney replacement therapy.
Can my patient with eGFR below 30 have gadolinium contrast?
With a group II agent, ACR and NKF advise that a clinically indicated examination should not be withheld. Group I agents should be avoided. Always follow local policy.
Why does my lab report a different eGFR?
Labs may use an older equation (MDRD or CKD-EPI 2009), round differently, or report "> 90" or "> 60". SpinCalc uses CKD-EPI 2021 with IDMS-standardised creatinine.
Why are my eGFRcr and eGFRcys so different?
Creatinine depends on muscle mass and diet; cystatin C on thyroid status, steroids and inflammation. A gap of 30% or more suggests one of these. The combined estimate is the most reliable.
Can I install SpinCalc as an app?
Yes. Use Install app in the header (or the menu on a phone). On iPhone/iPad, use Share → Add to Home Screen in Safari.
I found a bug or calculation error — how do I report it?
Email info@mrispin.com with the tool, the inputs and the result. We take accuracy seriously.
SpinCalc is the renal function calculator suite of MRISpin.com, developed by Fahad Joman and powered by PSM.
Every equation follows its original publication and current guidelines. Race coefficients are not used, in line with the 2022 NKF-ASN recommendations.
Disclaimer: For professional reference and education only. Not a substitute for clinical judgement, laboratory confirmation or specialist advice.