- Select the creatinine units (Conventional mg/dL or SI µmol/L) to match your lab report. Switching units clears those fields.
- Enter the urine creatinine concentration from the 24-hour urine specimen.
- Enter the 24-hour urine volume in mL (total volume collected over the full 24-hour period).
- Enter the serum creatinine — use the same units as the urine creatinine.
- Optionally enter height (cm) and weight (kg) to also receive the BSA-normalized CrCl (mL/min/1.73 m²).
- The result shows unadjusted CrCl, and if height and weight are provided, BSA-normalized CrCl alongside an expected-excretion adequacy check.
All computation runs in your browser; no values are stored or transmitted.
When to Use
Use this calculator when you have a completed 24-hour urine collection and want to quantify measured creatinine clearance (mCrCl). The 24-hour urine CrCl serves as a direct confirmation of kidney function when estimated GFR (eGFR) may be unreliable — for example in extremes of muscle mass, malnutrition, amputation, or when a precise functional measurement is needed before a major clinical decision.
Appropriate uses
Confirming eGFR in borderline CKD staging; assessing kidney function before living kidney donation evaluation; monitoring nephrotoxin exposure; evaluating completeness of a urine collection; patients with atypical body composition where creatinine-based estimates are unreliable. BSA normalization (mL/min/1.73 m²) allows comparison with eGFR values.
Limitations to know upfront
Measured CrCl systematically overestimates true GFR by 10–40% because creatinine is secreted by renal tubules in addition to being filtered — the overestimation is proportionally greater at lower GFR. An incomplete collection (common) falsely lowers the result. Always cross-check the collection adequacy using expected daily creatinine excretion before acting on the result.
Pearls & Pitfalls
Cross-check collection adequacy
Expected 24-hour creatinine excretion: approximately 20–25 mg/kg/day in men and 15–20 mg/kg/day in women. If the measured excretion is substantially lower, the collection is likely incomplete — results from an incomplete collection underestimate true CrCl. Enter height and weight to see the adequacy check.
CrCl overestimates GFR — intentionally
Tubular secretion of creatinine adds to the filtered load, so measured CrCl is typically 10–40% higher than the true GFR. This overestimation is useful in some clinical contexts (e.g., confirming adequate filtration for nephrotoxic drugs) but means mCrCl cannot be used interchangeably with eGFR for CKD staging thresholds, which are calibrated to true GFR.
Common pitfalls
(1) Incomplete urine collection is the most frequent error — always check expected creatinine excretion. (2) Non-steady-state creatinine (e.g., AKI, rapidly progressive disease) invalidates the result. (3) Certain drugs (cimetidine, trimethoprim) reduce tubular secretion of creatinine and will narrow the CrCl–GFR gap. (4) BSA normalization is meaningful for comparisons but adds BSA estimation error; Mosteller formula is used here.
Why Use It
In most clinical situations, CKD-EPI eGFR adequately estimates kidney function without the inconvenience of a 24-hour urine collection. However, a direct measurement becomes valuable when eGFR may mislead: patients with extreme muscle mass (athletes, sarcopenia), amputees, rapidly changing creatinine, borderline staging decisions, or pre-donation workup. The 24-hour urine CrCl provides a measurement-based anchor that can confirm or refute the estimated value and guide management when precision matters most.
Measured CrCl Calculator — 24-Hour Urine
Enter urine creatinine, 24-hour urine volume, and serum creatinine to calculate measured CrCl. Add height and weight to receive a BSA-normalized result and a collection-adequacy check.
⚕ Formula: CrCl (mL/min) = (UCr × Uvol) ÷ (SCr × 1440). UCr and SCr must share the same units (mg/dL or µmol/L); Uvol in mL; 1440 = minutes per day. BSA (Mosteller) = √(height cm × weight kg ÷ 3600). BSA-normalized CrCl = CrCl × 1.73 ÷ BSA. Measured CrCl overestimates true GFR by 10–40% due to tubular secretion of creatinine. For clinical decisions, confirm against eGFR and assess collection completeness. Requires physician interpretation.
Next Steps
Use the result to support — not replace — clinical judgment.
- Always verify collection adequacy using expected creatinine excretion before acting on the result. A low measured excretion suggests incomplete collection.
- Compare measured CrCl with CKD-EPI eGFR; if they diverge significantly, investigate the reason (incomplete collection, unusual muscle mass, drugs affecting secretion).
- Remember that measured CrCl overestimates true GFR — for CKD staging and KDIGO thresholds, use eGFR derived from validated estimating equations.
- Trend serial measurements rather than acting on a single result; document collection conditions (start/end time, any missed voids).
- Refer to nephrology when CrCl suggests a different CKD stage than the eGFR, or when the measurement is needed for a high-stakes decision (donor evaluation, dose calculation for a high-risk drug).
Evidence & References
Formula
| Quantity | Equation |
|---|---|
| Measured CrCl (mL/min) | (UCr × Uvol mL) ÷ (SCr × 1440 min/day) — UCr and SCr in same units |
| BSA — Mosteller formula (m²) | √(height cm × weight kg ÷ 3600) |
| BSA-normalized CrCl (mL/min/1.73 m²) | CrCl × 1.73 ÷ BSA |
| SI conversion for creatinine | µmol/L ÷ 88.4 = mg/dL |
| Expected Cr excretion — men | 20–25 mg/kg/day (lower end in elderly) |
| Expected Cr excretion — women | 15–20 mg/kg/day (lower end in elderly) |
CrCl vs. GFR interpretation
| Measured CrCl (mL/min) | Approximate GFR range | Clinical context |
|---|---|---|
| ≥ 90 | ≥60–90 true GFR | Normal to mildly reduced; recall 10–40% overestimation |
| 60–89 | ~45–75 true GFR | Consistent with CKD G2–G3a range; verify with eGFR |
| 30–59 | ~20–50 true GFR | CKD G3b–G4 range; significant impairment |
| < 30 | <20 true GFR | Advanced CKD; specialist management indicated |
These ranges are approximate because the CrCl–GFR gap varies with GFR (wider at low GFR) and with medications affecting tubular secretion. Do not use measured CrCl as a direct substitute for eGFR in KDIGO staging without accounting for the systematic overestimation.
References
- Cockcroft DW, Gault MH. Prediction of Creatinine Clearance from Serum Creatinine. Nephron. 1976;16(1):31–41.
- Stevens LA, Levey AS. Measured GFR as a Confirmatory Test for Estimated GFR. J Am Soc Nephrol. 2009;20(11):2305–2313.
- Kidney Disease: Improving Global Outcomes (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.
