Creatinine clearance: calculation with 24-hour urine, body surface area correction and Cockcroft-Gault
What creatinine clearance measures and when it is used
Creatinine clearance is the volume of plasma the kidneys clear of creatinine per unit of time, in mL/min. Because creatinine is freely filtered by the glomeruli and little reabsorbed, clearance is used as an approximation of the glomerular filtration rate (GFR).
The approximation is not perfect. Part of urinary creatinine comes from tubular secretion, which makes clearance overestimate the true filtration.
In routine practice, measured clearance requires a 24-hour urine collection and a serum creatinine. The KDIGO 2024 guideline considers timed collection highly prone to error and suggests using it when filtration measured with an exogenous marker is not available and the estimate based on creatinine and cystatin C seems inaccurate. For most situations, KDIGO recommends validated equations, such as the one in the CKD-EPI 2021 GFR calculator.
KDIGO 2024 cites situations that call for more accuracy than the creatinine-based estimate, such as the evaluation of kidney donor candidates and the dosing of drugs with a narrow therapeutic range. In addition, many older dose adjustment schemes were built on creatinine clearance.
How to calculate clearance in the calculator: required and optional inputs
The calculator has three required fields, the collection time and four optional fields.
Required (all greater than zero):
- Urine creatinine, in mg/dL, measured in the collected urine.
- Serum creatinine, in mg/dL, up to 30 mg/dL.
- Total collection urine volume, in mL.
The collection time is prefilled with 24 hours; change it if the collection lasted a different period (up to 48 hours). With these data, the tool shows the measured clearance (mL/min, one decimal place) and the minute volume (mL/min, two decimal places).
Optional:
- Weight (kg) and height (cm): allow calculation of body surface area (BSA) and the clearance corrected to 1.73 m², which comes with a category classification.
- Age (years) and biological sex, together with weight: allow clearance to be estimated with the Cockcroft-Gault formula. Age, from 18 to 120 years, is read as a whole number; 65.9 years is entered as 65.
Impossible values, such as zero, negative numbers or weight above 400 kg, produce a message saying which field to correct.
Formulas used: clearance, Mosteller BSA and Cockcroft-Gault
The calculator applies four equations in sequence, depending on the fields filled in.
CrCl (mL/min) = (UCr × V) ÷ (SCr × t)
Minute volume (mL/min) = V ÷ t
BSA (m²) = √[weight (kg) × height (cm) ÷ 3,600]
Corrected CrCl (mL/min/1.73 m²) = CrCl × 1.73 ÷ BSA
Cockcroft-Gault (mL/min) = [(140 − age) × weight] ÷ (72 × SCr) × 0.85 if female
- UCr: urine creatinine (mg/dL).
- SCr: serum creatinine (mg/dL).
- V: collection urine volume (mL).
- t: collection time in minutes (hours × 60; 1,440 in 24 hours).
- 1.73: reference body surface area, in m².
BSA uses the simplified Mosteller formula, published in the New England Journal of Medicine in 1987. The urine-free estimate comes from Cockcroft and Gault (1976): the formula was derived for adult men, with data from 249 patients aged 18 to 92, and the authors indicated a value 15% lower for women, hence the 0.85 factor.
Worked example with all fields filled in
Hypothetical case: urine creatinine 100 mg/dL, serum creatinine 1.2 mg/dL, volume of 1,500 mL in 24 hours, weight 70 kg, height 175 cm, age 65 years, male.
- Measured clearance: (100 × 1,500) ÷ (1.2 × 1,440) = 150,000 ÷ 1,728 = 86.8 mL/min.
- Minute volume: 1,500 ÷ 1,440 = 1.04 mL/min.
- BSA: √(70 × 175 ÷ 3,600) = √3.4028 = 1.84 m².
- Corrected clearance: 86.806 × 1.73 ÷ 1.8447 = 81.4 mL/min/1.73 m².
- Cockcroft-Gault: (140 − 65) × 70 ÷ (72 × 1.2) = 5,250 ÷ 86.4 = 60.8 mL/min.
The calculator returns exactly these values. The corrected clearance of 81.4 falls in the 60 to 89 range, and the tool shows “Category G2”, with the warning that the comparison with GFR categories is approximate. If the same urine had been collected over 12 hours, the clearance would double to 173.6 mL/min, which shows how much the entered time matters.
The difference between the measured clearance (86.8) and the Cockcroft-Gault estimate (60.8) is expected: they are different methods, and urine collection, muscle mass and tubular secretion affect each one differently.
How to understand the result and the categories shown
Standard clearance is given in mL/min, without adjustment for body size. Corrected clearance divides by the person's size and allows comparison with the filtration categories, which are expressed per 1.73 m².
When weight and height are available, the calculator classifies the corrected clearance using the KDIGO 2024 GFR categories:
| Category | mL/min/1.73 m² | KDIGO term |
|---|---|---|
| G1 | 90 or more | Normal or high |
| G2 | 60 to 89 | Mildly decreased |
| G3a | 45 to 59 | Mildly to moderately decreased |
| G3b | 30 to 44 | Moderately to severely decreased |
| G4 | 15 to 29 | Severely decreased |
| G5 | less than 15 | Kidney failure |
The KDIGO categories were defined for GFR, and applying them to corrected clearance is an approximation made by the tool. A single category does not define chronic kidney disease: KDIGO requires an abnormality of structure or function present for at least three months and also considers albuminuria. Interpretation is up to the healthcare professional.
Common collection and calculation errors, with checklist
The biggest source of error in clearance is the urine collection, not the calculation.
- Incomplete collection: missing one void reduces the volume and underestimates clearance.
- Wrong time: the formula divides by the actual time; a 22- or 26-hour collection recorded as 24 distorts the result. Enter the correct collection time.
- Mixed units: urine creatinine in mg/24 h or in mmol/L does not go in the mg/dL field. Creatinine in µmol/L converts to mg/dL by dividing by 88.4 (KDIGO 2024 factor).
- Volume in liters: 1.5 L entered as 1.5 mL lowers the result a thousandfold.
- Serum creatinine from another day: blood should be drawn during the collection period.
- Weight with edema or obesity: changes BSA and Cockcroft-Gault.
Checklist:
- Is the collection time entered the actual one, with the first urine discarded and the last included?
- Volume in mL, creatinines in mg/dL?
- Is the serum creatinine from the same period?
- Is the result consistent with the expected creatinine excretion for the weight?
- To compare with categories, was the value corrected to 1.73 m² used?
Limitations and comparison with estimated GFR and Cockcroft-Gault
Measured creatinine clearance has two structural limitations: it depends on a collection that is hard to do well, and it overestimates filtration because of tubular creatinine secretion. KDIGO 2024 classifies it as highly prone to error.
| Method | Data | Use described in the sources |
|---|---|---|
| Measured clearance (24 h) | Serum and urine creatinine, volume | When estimates seem inaccurate and there is no measured GFR (KDIGO 2024) |
| Cockcroft-Gault | Creatinine, age, weight, sex | Basis of many older drug labels; developed before creatinine standardization (KDIGO 2024) |
| CKD-EPI 2021 | Creatinine, age, sex | Equation recommended by the NKF for adults |
| MDRD | Creatinine, age, sex | Earlier equation; less accurate above 60 mL/min/1.73 m² |
For drug dosing, KDIGO 2024 considers validated creatinine-based equations adequate in most cases, and notes that drug clearance relates better to non-indexed GFR. Also compare with the GFR by MDRD. The same 24-hour urine allows measurement of 24-hour urine protein.
Frequently asked questions about creatinine clearance
What is the difference between measured clearance and corrected clearance?
Measured clearance is the volume cleared per minute, in mL/min, without adjustment. Corrected clearance divides by body surface area and multiplies by 1.73 m², which allows comparison between people of different sizes and use of the KDIGO categories.
Do I need to fill in weight, height, age and sex?
No. Only urine creatinine, serum creatinine and collection volume are required, and the time is prefilled with 24 hours. Weight and height unlock the corrected clearance and the classification; age, weight and sex unlock the Cockcroft-Gault estimate.
Why did the measured clearance and the Cockcroft-Gault value differ?
Because they are different methods. Measured clearance depends on the urine collection and tubular secretion; Cockcroft-Gault estimates from age, weight and serum creatinine. In the original study, the correlation between estimated and measured values was 0.83, that is, good but not perfect.
How do I know whether the 24-hour collection was complete?
Check the start and end times, whether any void was missed and whether the total creatinine excreted during the day is consistent with the person's weight and muscle mass. If in doubt, the laboratory will advise a new collection.
Is creatinine clearance better than estimated GFR?
Not in most cases. KDIGO 2024 recommends validated equations, such as CKD-EPI, and reserves timed collection for situations where estimates seem inaccurate and no measured GFR is available.
Can the calculator be used for children?
The measured clearance formula applies at any age, but Cockcroft-Gault was developed in adults and the categories shown are for adults. In pediatrics, use specific equations and references.
References
- Cockcroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine. Nephron. 1976;16(1):31-41. View
- Mosteller RD. Simplified calculation of body-surface area. N Engl J Med. 1987;317(17):1098. View
- 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. View
- Levey AS, Coresh J, Greene T, Stevens LA, Zhang YL, Hendriksen S, et al. Using standardized serum creatinine values in the modification of diet in renal disease study equation for estimating glomerular filtration rate. Ann Intern Med. 2006;145(4):247-54. View
Updated . A support tool for educational purposes; it does not replace clinical assessment.