Creatinine Clearance Calculator
Estimate glomerular filtration rate (GFR) using standard clinical equations
CKD-EPI vs Cockcroft-Gault
Use CKD-EPI for staging chronic kidney disease and assessing nephrology referral needs. Use Cockcroft-Gault for medication dosing decisions – most drug dosing guidelines still reference this method.
CKD-EPI gives more accurate results in patients with normal kidney function and eliminates some of the age-related overestimation seen with Cockcroft-Gault. For patients over 65 with borderline results, CKD-EPI provides better clinical correlation.
Quick Reference
| CKD Staging | CKD-EPI |
| Drug Dosing | Cockcroft-Gault |
| Contrast Risk Assessment | CKD-EPI |
| Nephrology Referral | CKD-EPI |
Dose Adjustments for Common Medications
Check these thresholds against your Cockcroft-Gault result for dose modifications:
| Medication | Threshold (mL/min) | Action |
|---|---|---|
| Digoxin | <60 | Reduce dose by 50% |
| DOACs | <50 | Reduce dose or avoid |
| Gabapentin | <60 | Adjust dosing interval |
| Lithium | <90 | Monitor levels closely |
| Aminoglycosides | Any decrease | Extended interval dosing |
| Metformin | CKD-EPI <30 | Discontinue |
Checking Lab Values for Errors
Double-check results that seem inconsistent with clinical presentation. A 25-year-old athlete with creatinine 1.8 mg/dL may have normal function due to high muscle mass, while an elderly person with sarcopenia and creatinine 1.0 mg/dL may have significant kidney impairment.
Wait 24-48 hours after creatinine-affecting events before calculating GFR. Recent contrast exposure, dehydration, ACE inhibitor initiation, or muscle injury can temporarily alter creatinine without reflecting actual GFR changes.
Red Flags
Recalculate if you see:
- Creatinine <0.4 mg/dL in adults (possible dilution error)
- GFR >150 in patients over 65 (likely overestimate)
- Results inconsistent with previous stable values
- Unit errors: 200 μmol/L = 2.3 mg/dL, not 200 mg/dL
Normal GFR Decline with Age
Expect GFR decline of 6-10 mL/min/1.73m² per decade after age 40. A 75-year-old with GFR 65 may have normal function for their age. Don’t automatically label elderly patients with mild reductions as having CKD without additional evidence.
Pediatric patients need different formulas – these adult equations are inaccurate under age 18. Use the Schwartz equation or refer to pediatric nephrology for patients under 18.
GFR Thresholds and Actions
GFR >60
Annual monitoring if diabetes/hypertension present. Screen for proteinuria. No dose adjustments typically needed.
GFR 30-60
Monitor every 3-6 months. Screen for anemia, bone disease. Consider nephrology referral. Review all medications.
GFR 15-30
Monthly monitoring. Nephrology care essential. RRT education. Extensive medication review required.
GFR <15
Prepare for dialysis or transplant. Symptom management priority. Palliative care discussion if appropriate.
How Often to Retest
Stable CKD patients with GFR 30-60: every 3-6 months. Progressive decline or GFR <30: monthly or more frequent. Acute changes warrant immediate repeat testing within 48-72 hours.
| Stage | Frequency | Additional Tests |
|---|---|---|
| G1-G2 | Annually | Urine albumin, BP monitoring |
| G3a | Every 6 months | CBC, phosphorus, PTH |
| G3b | Every 3-4 months | CBC, mineral metabolism |
| G4 | Every 1-3 months | Full CKD panel, RRT planning |
| G5 | Monthly or more | Electrolytes, acid-base status |
Cystatin C and 24-Hour Collections
Order cystatin C when muscle mass abnormalities make creatinine unreliable – amputees, bodybuilders, patients with sarcopenia, or those with muscular dystrophy. Cystatin C equations avoid creatinine-related estimation errors.
24-hour urine collection provides gold standard accuracy but requires complete collection compliance. Reserve for living donor evaluation, clinical trials, or when estimation equations seem clearly incorrect.
Nuclear GFR measurement offers highest accuracy but involves radiation and specialized facilities. Use only when precise measurement significantly affects treatment decisions – research protocols or donor evaluation.
When Standard Equations Fail
Consider cystatin C or measured clearance if:
- Extreme body composition (BMI <15 or >40)
- Vegetarian diet or creatine supplementation
- Amputation or paralysis
- Results inconsistent with clinical picture
- Cirrhosis or severe liver disease