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 guidelines recommend reflex cystatin C when creatinine eGFR 45–59 |
| 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, 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
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.
Complete guide to the MRISpin Renal Calculator Suite — what each tool does, when to use it, and how to interpret results.
The MRISpin Renal Calculator Suite provides four validated equations for estimating kidney function. All calculators run entirely in your browser — no data is sent to any server.
Use the sidebar to switch between calculators. The Compare All tool lets you run all four equations side-by-side from a single set of inputs.
What it is: The 2021 CKD-EPI creatinine equation is the current international standard for estimating glomerular filtration rate (GFR) in adults. It replaced the 2009 version by removing the race coefficient, making it applicable to all patients regardless of race or ethnicity.
When to use it: CKD staging, monitoring of kidney function over time, and identifying patients who may need nephrology referral. This is the equation your laboratory most likely reports.
Inputs required:
| Biological sex | Male or Female — determines the creatinine threshold and exponent |
| Age | In years (18–120). Age affects the annual GFR decline factor (0.9938Age) |
| Serum creatinine | In mg/dL or µmol/L (auto-converted). Must be IDMS-standardised |
How to interpret the result: The eGFR value maps to a CKD stage (G1–G5). A single result is insufficient to diagnose CKD — the same result must be present for ≥ 3 months. Always consider albuminuria alongside eGFR for full CKD staging.
Not valid in: Acute kidney injury (rising/unstable creatinine), pregnancy, patients under 18, organ transplant recipients, or patients with extreme muscle mass (e.g. amputees, bodybuilders, severe sarcopenia).
What it is: The Cockcroft-Gault equation (1976) estimates creatinine clearance (CrCl) — not true GFR. It remains the standard used by drug manufacturers when defining renal dose adjustments in drug labelling and package inserts.
When to use it: Whenever you need to adjust a medication dose based on renal function. Do not use it for CKD staging — use CKD-EPI eGFR for that.
Inputs required:
| Biological sex | Female result is multiplied by 0.85 |
| Age | In years. Older patients produce less creatinine, raising CrCl |
| Body weight | In kg or lbs (auto-converted). Use actual body weight (ABW) by default |
| Serum creatinine | In mg/dL or µmol/L (auto-converted) |
Weight guidance: Use ABW for most patients. In obese patients (ABW > 30% over IBW), many drug guidelines recommend using Ideal Body Weight (IBW) or Adjusted Body Weight (AdjBW). Always check the specific drug monograph.
Note: CrCl overestimates true GFR by ~10–20% due to tubular secretion of creatinine. In elderly or malnourished patients with low muscle mass, low serum creatinine may cause CrCl to be overestimated.
What it is: The 2021 CKD-EPI cystatin C equation estimates GFR using serum cystatin C instead of creatinine. Cystatin C is a small protein produced by all nucleated cells and freely filtered by the glomerulus — its serum level is less affected by muscle mass or diet than creatinine.
When to use it: When creatinine-based eGFR may be unreliable — e.g. sarcopenia, malnourishment, extreme body composition, vegetarian diet, or as confirmatory testing when creatinine eGFR is 45–59 (KDIGO recommends reflex cystatin C in this range to confirm or exclude CKD G3a).
Inputs required:
| Age | In years (18–120) |
| Biological sex | Female result is multiplied by 0.932 |
| Serum cystatin C | In mg/L. Must be measured with an IFCC-standardised assay. Normal range: 0.51–0.98 mg/L |
Confounders: Cystatin C is elevated by hypothyroidism and corticosteroid use, and lowered by hyperthyroidism — independent of GFR. Results must be interpreted carefully in these contexts.
What it is: The Modification of Diet in Renal Disease (MDRD) 4-variable equation was the dominant GFR estimation method from 1999 until the CKD-EPI 2009/2021 equations replaced it. The race coefficient originally in the formula has been removed here per 2021 NIDDK/NKF guidance.
When to use it: Primarily for historical comparison, reconciliation with older lab reports, or when a lab system still reports MDRD. Do not use for current clinical CKD staging — use CKD-EPI 2021 instead.
Key limitation: MDRD systematically underestimates GFR when eGFR > 60 mL/min/1.73 m². This means it overcategorises patients into lower CKD stages when kidney function is relatively preserved.
Inputs required: Biological sex, age (years), and serum creatinine (IDMS-standardised, mg/dL or µmol/L).
What it does: Runs all four equations simultaneously from a single input set and displays results side-by-side in both a card view and a summary table. Useful for comparing estimates, understanding inter-equation differences, or teaching purposes.
Optional inputs: Body weight is only required for the Cockcroft-Gault CrCl. Cystatin C is only required for the CKD-EPI Cystatin C eGFR. If these are left blank, those calculations are skipped and shown as "not calculated".
Interpreting differences: It is normal for the four equations to give different results. CKD-EPI 2021 is the most accurate overall. MDRD tends to be lower when GFR is preserved. CrCl is higher than eGFR due to tubular creatinine secretion. Cystatin C results may differ when muscle mass confounds creatinine.
All primary equations, clinical guidelines, and unit conversion sources used in this calculator suite.
Inker LA, Eneanya ND, Coresh J, Peralta CA, Schmid CH, Feldman HI, Hsu CY, Greene T, Karger AB, Navaneethan SD, Okparavero A, et al. New Creatinine- and Cystatin C–Based Equations to Estimate GFR without Race. New England Journal of Medicine. 2021;385(19):1737–1749.
DOI: 10.1056/NEJMoa2102953 · PMID: 34554658
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, Greene T, Rogers N, Roth D. A more accurate method to estimate glomerular filtration rate from serum creatinine: a new prediction equation. Modification of Diet in Renal Disease Study Group. Annals of Internal Medicine. 1999;130(6):461–470.
DOI: 10.7326/0003-4819-130-6-199903160-00002 · PMID: 10075613
Levey AS, Coresh J, Greene T, Marsh J, Stevens LA, Kusek JW, Van Lente F; Chronic Kidney Disease Epidemiology Collaboration. Expressing the Modification of Diet in Renal Disease Study equation for estimating glomerular filtration rate with standardized serum creatinine values. Clinical Chemistry. 2007;53(4):766–772.
DOI: 10.1373/clinchem.2006.078287 · PMID: 17332152
Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2012 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney International Supplements. 2013;3(1):1–150.
National Kidney Foundation and American Society of Nephrology Task Force on Reassessing the Inclusion of Race in Diagnosing Kidney Disease. A New Academic Consortium Recommendation for Including Race in the Estimation of Kidney Function. American Journal of Kidney Diseases. 2021;78(5):696–706.
PMID: 34563598
National Kidney Foundation. CKD Evaluation and Management. 2022. kidney.org — KDOQI CKD Guidelines
Creatinine unit conversion: 1 mg/dL = 88.4 µmol/L
Source: Levey AS, Greene T, Kusek JW, Beck GL. A simplified equation to predict glomerular filtration rate from serum creatinine. Journal of the American Society of Nephrology. 2000;11:A0828.
IDMS standardisation: 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. Clinical Chemistry. 2006;52(1):5–18. PMID: 16391889
Cystatin C standardisation (IFCC): Grubb A, Blirup-Jensen S, Lindström V, et al. First certified reference material for cystatin C in human serum ERM-DA471/IFCC. Clinical Chemistry and Laboratory Medicine. 2010;48(11):1619–1621. PMID: 20704545
Get in touch with the MRISpin team for questions, bug reports, or feedback about the Renal Calculator Suite.
Is my patient data stored or sent anywhere?
No. All calculations run entirely in your browser using JavaScript. No patient data is transmitted to any server, stored, or logged at any point.
Which equation should I use for CKD staging?
Use eGFR (CKD-EPI 2021) for CKD staging and monitoring — it is the current international standard recommended by KDIGO, NIDDK, NKF, and most nephrology guidelines.
Which equation should I use for drug dosing?
Use CrCl (Cockcroft-Gault) for renal drug dose adjustment. Most drug package inserts and pharmacokinetic studies use CrCl, not eGFR, as the basis for dosing thresholds.
Why is my MDRD result lower than CKD-EPI?
This is expected. MDRD systematically underestimates GFR when eGFR > 60 mL/min/1.73 m². This was one of the main reasons CKD-EPI was developed to replace it. The difference is typically small at lower GFR values.
My lab reports a different eGFR — why?
Labs may use older equations (e.g. MDRD), different creatinine assays, or race-adjusted variants. The CKD-EPI 2021 equation used here is race-free and requires IDMS-standardised creatinine. Confirm with your laboratory which equation and creatinine assay they use.
I found a bug or calculation error — how do I report it?
Please contact us at [email protected] with the input values you used and the result you received. We take accuracy seriously and will investigate promptly.
The MRISpin Renal Calculator Suite was developed by Fahad J. and is powered by PSM. It is part of the MRISpin platform at mrispin.com.
All equations are implemented according to their original published sources and current clinical guidelines. The race coefficient has been removed from the MDRD equation in line with 2021 NKF/NIDDK recommendations.
Disclaimer: This tool is for educational and clinical reference purposes only. It is not a substitute for professional clinical judgement, laboratory confirmation, or specialist consultation. Results should always be interpreted in the context of the patient's complete clinical presentation.