Creatinine clearance: what it is, values ​​and calculator

The creatinine clearance formula is used to evaluate kidney function by inferring the glomerular filtration rate, and can be calculated using creatinine measured in the blood or urine collected over 24 hours, which compares the concentration of creatinine in the blood with the amount that is eliminated in the urine.

Generally, the 24-hour urine creatinine clearance test is requested when a change in the concentration of creatinine in the blood and/or an increase in the amount of protein in the urine is noted, being useful to assist in the diagnosis of kidney diseases. Due to the difficulty of properly collecting this test, it is used less and less. Blood creatinine clearance is performed using formulas using the patient’s creatinine and age.

Read too: Creatinine: what it is, reference values ​​and when to take the test

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The test result indicates the amount of creatinine that was removed from the blood and eliminated in the urine, and as this process is carried out by the kidneys, changes in the results may be indicative of kidney damage.

Creatinine clearance calculator

To find out your creatinine clearance, enter your creatinine result into the following calculator:

Currently, the most recommended formula to be used to calculate creatinine clearance is the CKD-EPI, which considers the patient’s blood creatinine value, age and sex. Another formula to check creatinine clearance is Cockcroft & Gault formula, where Creatinine clearance = ((140 – age in years) x weight (in kg)) / 72 x plasma creatinine (mg/ dL). If the calculation is made for a female person, the result must be multiplied by 0.85.

The formulas for calculating creatinine clearance may vary according to the laboratory, with the test result indicating the reference value and the method used, currently recommending the use of the CPK-EPI formula.

Reference values

Creatinine clearance reference values ​​may vary according to the formula used in the laboratory to make the calculation, which may be:

• Superior a 90 mL/min/1,73 m²if creatinine clearance was calculated using the formula CKD-EPI;
• 70 a 130 mL/min/1,73 m²in the case of children and calculation using the formula Cockcroft & Gault;
• 85 a 125 mL/min/1,73 m²in the case of women and calculation using the formula Cockcroft & Gault;
• 75 a 115 mL/min/1,73 m²in the case of men and calculation using the formula Cockcroft & Gault.

Therefore, it is important to pay attention to the test results to know the formula used by the laboratory and also to better understand the result.

What is it for

The creatinine clearance test is used to assess kidney function. Furthermore, creatinine clearance can also be used to assess the evolution of any renal alteration and the response to the treatment indicated by the doctor.

When is indicated

Creatinine clearance must be calculated whenever the doctor receives the creatinine result from the laboratory, and is essential when some signs and symptoms are noticed, such as:

• Swelling in the body;
• Urine with blood or foam;
• Decrease in the amount of urine produced during the day;
• Constant pain in the lower back.

This test can be carried out routinely or after a change in blood creatinine levels or an increase in the amount of protein in the urine has been identified.

How to take the exam

To take the 24-hour urine creatinine clearance test, it is not necessary to carry out any preparation, you just need to follow the doctor’s and/or laboratory’s instructions regarding urine collection. It is recommended to discard the first stream of urine of the day, as it is more concentrated, and collect it as directed.

In the case of 24-hour urine, it is recommended that all urine produced during the day be collected, with the last urine being collected at the same time as the first urine collection. See more details on how the urine test is collected.

Along with collecting urine, it is necessary to measure creatinine in the blood, since the calculation of creatinine clearance can take into account the concentration of this protein in the blood.

Low creatinine clearance

Low creatinine clearance is typically indicative of kidney problems, such as chronic kidney disease.

Therefore, it is important that the doctor evaluates the creatinine clearance result together with the results of other tests and taking into account the person’s age, health history and lifestyle habits.

High creatinine clearance

Elevated creatinine clearance values ​​may be noticed in pregnant women, after physical activity or in the initial kidney damage caused by diabetes, which causes glomerular hyperfiltration, for example. In these cases, it is important for the doctor to evaluate the result taking into account the results of other tests that may have been requested.

Currently, another molecule called cystatin C can be measured in the blood and used to calculate renal clearance, in this case cystatin C clearance. This molecule suffers less interference from other external factors that alter the creatinine value, such as diet, patient weight and use of medications. More recently, a calculator that incorporates creatinine and cystatin C was launched, called CKD-EPI creatinine-cystatin C, which is more accurate than the previous ones.