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Kidney Function Calculators — eGFR, Creatinine Clearance & GFR Estimates
Use our free tools to estimate kidney function: an eGFR calculator (CKD-EPI), creatinine clearance (Cockcroft-Gault) and comparison to MDRD. This page explains what those numbers mean, shows how clinicians interpret results, and provides clear next steps if results are low. The calculators are for informational use only — always confirm with your healthcare provider.
Note: We calculate CKD-EPI eGFR (race-free 2021 variant where applicable) for a standardized interpretation and show Cockcroft-Gault creatinine clearance for drug-dose considerations. Laboratories and guidelines may use slightly different reporting rules — always refer to your lab report and clinician. (Sources: NKF, KDIGO).
Why measure GFR? Key takeaways
- eGFR is the routine, standardized estimate of kidney filtering function and is reported in mL/min/1.73 m².
- Values <60 mL/min/1.73 m² on repeated testing generally indicate reduced kidney function (CKD) and warrant follow-up.
- Cockcroft-Gault (creatinine clearance) estimates drug clearance (mL/min) and is still used for medication dosing in many formularies.
- CKD staging requires combined assessment of eGFR and albuminuria — do not interpret eGFR alone.
Which equations do clinicians use?
The most commonly used estimating equations are CKD-EPI (recommended and increasingly reported in a race-free 2021 form), MDRD, and for creatinine clearance dosing, Cockcroft-Gault. CKD-EPI is generally more accurate than MDRD across a range of populations and is preferred for clinical reporting. CKD-EPI (2021) and guideline bodies provide implementation guidance.
Comparison table — CKD-EPI vs MDRD vs Cockcroft-Gault
| Method | What it estimates | When to use (pros / cons) |
|---|---|---|
| CKD-EPI (creatinine, 2009 / 2021 race-free) | Standardized eGFR (mL/min/1.73 m²) from serum creatinine, age, sex (2021 removes race coefficient). | Pros: More accurate than MDRD in many groups; preferred for clinical reporting. Cons: Still an estimate — affected by muscle mass & lab standardization. |
| MDRD | eGFR estimate used historically; works reasonably at lower GFR ranges. | Pros: Widely validated historically. Cons: Less accurate at higher GFRs vs CKD-EPI; many labs now prefer CKD-EPI. |
| Cockcroft-Gault (CrCl) | Creatinine clearance (mL/min) — used historically for drug dosing; requires weight. | Pros: Useful for drug dosing guidelines still tied to CrCl. Cons: Not standardized to BSA; less accurate when creatinine assays are standardized; many dosing guidelines now accept eGFR conversions. |
Real-world interpretation examples
Example A — single lab result
Lab reports eGFR 55 mL/min/1.73 m² (no albuminuria). This falls into CKD Stage 3a range; clinician will usually repeat testing and check urine albumin, blood pressure, medication list, and metabolic causes before diagnosing CKD.
Example B — drug dosing
Older drug guidelines use creatinine clearance. If Cockcroft-Gault estimates CrCl 42 mL/min, the prescribing clinician may reduce dose per the drug monograph — but modern practice increasingly uses standardized eGFR conversions with clinical judgement.
Pros & Cons — quick summary
Pros
- eGFR provides an accessible, standardized measure to screen and monitor kidney function.
- Equations (CKD-EPI) are validated across many populations and incorporated into lab reporting.
Cons
- All estimates assume stable creatinine and are influenced by muscle mass, diet, and medications.
- Single low eGFR results should be repeated; albuminuria and clinical context are needed for accurate staging.
Expert tips for accurate interpretation
- Always compare eGFR with prior values — look for trends, not one-off numbers.
- If muscle mass is unusually low or high (e.g., amputees, bodybuilders), eGFR may misestimate true GFR — discuss cystatin C testing with your clinician.
- Review current medications (NSAIDs, aminoglycosides, ACEi/ARBs) that can affect kidney function or lab results.
- For drug dosing, state whether the guideline wants CrCl (Cockcroft-Gault) or eGFR — clarify with pharmacist/clinician when in doubt.
Common mistakes people make
- Interpreting a single eGFR result as definitive CKD without repeat testing or albuminuria assessment.
- Using unstandardized creatinine values (e.g., older lab methods) without noting the assay standardization.
- Decision-making on dosing without checking which measure (CrCl vs eGFR) the drug guideline requires.
Internal linking opportunities (5–7)
- Blood Sugar Calculator — link when discussing diabetic kidney disease risk and glucose control.
- Cardiovascular Risk Calculator — CKD increases CV risk; cross-link for comorbidity context.
- BMI Calculator — obesity and weight management affect renal risk and dosing.
- BMR Calculator — for nutrition / energy planning in CKD dietary management.
- Privacy Policy — keep visible near forms and inputs for transparency.
- Body Fat Calculator — optional, when discussing muscle mass influencing creatinine.
Advanced FAQ — eGFR, clearance & kidney function
Frequently Asked Questions
Q1: What is the difference between eGFR and creatinine clearance?
A: eGFR estimates filtration standardized to body surface area (mL/min/1.73 m²) using CKD-EPI or MDRD equations. Creatinine clearance (CrCl) — often from Cockcroft-Gault — estimates unindexed clearance (mL/min) and historically guided drug dosing.
Q2: Which equation should my lab report — CKD-EPI or MDRD?
A: Many labs now report CKD-EPI (preferred because of improved accuracy), often using the 2021 race-free variant. Check your lab note or ask your clinician which equation was used for the reported eGFR.
Q3: Do I have kidney disease if my eGFR is 58?
A: eGFR 45–59 mL/min/1.73 m² is Stage 3a range. A single value is not diagnostic — your clinician will repeat tests, check urine albumin (protein), and evaluate history before confirming CKD.
Q4: How do medications change eGFR readings?
A: Some drugs alter creatinine secretion (e.g., trimethoprim, cimetidine) or cause true changes in kidney function (e.g., NSAIDs). Always review the medication list with your clinician when interpreting a change in eGFR.
Q5: When is cystatin C useful?
A: Cystatin C–based eGFR (or combined creatinine+cystatin C equations) is valuable when creatinine is unreliable (abnormal muscle mass, recent muscle events, or suspected assay interference). It improves accuracy in many cases.
Q6: What thresholds trigger nephrology referral?
A: Persistent eGFR <60 mL/min/1.73 m², rapidly declining eGFR, or significant albuminuria generally prompt specialist referral. Clinical context and guideline thresholds vary; discuss with your clinician.
Q7: Can diet or dehydration temporarily change eGFR?
A: Yes — dehydration raises creatinine and lowers eGFR temporarily. High-protein meals, extreme exercise, or certain supplements can also affect serum creatinine. Repeat testing when the patient is euvolemic for accurate assessment.
Q8: How does body surface area (BSA) indexing affect interpretation?
A: eGFR is indexed to a standard BSA (1.73 m²). For drug dosing or individuals with very small or large body surface areas, clinicians may use non-indexed values or adjust calculations accordingly.
Q9: Are there population groups where eGFR is less accurate?
A: Yes — extremes of muscle mass, recent acute illness, pregnancy, and some ethnic groups may have different creatinine kinetics. In those situations, cystatin C or measured GFR methods may be preferred.
Q10: What is MDRD calculator and when is it still used?
A: MDRD is an older creatinine-based estimating equation; it remains familiar and used in historical datasets, but many labs and guidelines now prefer CKD-EPI for routine reporting.
Key next steps if results are low
- Repeat the blood test to confirm low eGFR and check urine albumin (UACR) to stage CKD properly.
- Review medicines, hydration status, blood pressure, and glucose control (diabetics).
- Discuss results with a clinician — consider referral to nephrology if persistent or progressive.