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Creatinine Clearance: Examination Evaluates Kidney Function

Creatinine Clearance: Examination Evaluates Kidney Function

Creatinine clearance is used to assess kidney function. It is used to help diagnose kidney dysfunction. The test is a comparison between the creatinine level in the blood and the levels of this substance in the urine.

Creatinine is a residue produced by the breakdown of a protein called creatine phosphate. This protein acts on the functioning of muscles, being obtained through foods rich in protein. The muscles are in constant activity, and therefore consuming creatine phosphate all the time. When broken to aid muscle function, creatine phosphate produces a residue called creatinine, which is filtered in the kidneys and excreted in the urine. Approximately 2% of the creatine present in the body is converted to creatinine every day.

When the kidneys are not working well creatinine filtration is compromised. This means that much of the creatinine produced will not be excreted in the urine, remaining in the blood.

The creatinine clearance therefore shows how much creatinine is being produced (blood) and how much creatinine is being excreted (urine). This helps to understand if kidney function is even compromised, as some people may have lower or higher levels of creatinine in the blood without presenting problems in function - and urine sample results prove that creatinine is adequately filtered .


Creatinine clearance helps detect renal failure in early stages. Therefore, the test is indicated for people who:

  • Have a family or personal history of chronic kidney disease
  • Have diseases that increase the risk of kidney problems such as diabetes, hypertension, obesity, polycystic kidneys, glomerulonephritis, urinary tract infections of repetition and renal calculi of repetition
  • Use of medicines that alter renal function
  • Are older than 50 years
  • Are smokers

Other symptoms and conditions that may justify screening with a creatinine test are:

  • Body blows without a definite cause
  • Anemia without apparent cause
  • Severe heart disease
  • Blood in urine
  • Urine with foam
  • Unintentional weight loss
  • Loss of appetite, and weakness with no apparent cause
  • Children with growth problems.

Creatinine clearance is especially useful for people who have blood creatinine levels that are naturally above or below the reference values. Elderly, for example, they have less muscle mass and therefore use less creatine phosphate, thus producing less creatinine. In such cases, a blood test may only erroneously point to results within the reference values. But if this blood test is compared to the amounts of creatinine that are being excreted in the urine, it is possible to average - since people whose kidneys are not functioning properly will have an even smaller amount of creatinine in the urine, indicating that it does not is being screened.


Because it is a common blood and urine test, there are no express contraindications for creatinine dosing.

Pregnant women can do?

Women during pregnancy are allowed to do the according to medical advice, and there is no express contraindication. However, the results may change - somewhat above normal - because of pregnancy.

Creatinine clearance is not a commonly requested exam during pregnancy, but can be used to follow women who already have a

For creatinine clearance a minimum fasting time of three hours is required for blood collection. The ideal is not to be in the menstrual period. As the urine is collected by the patient himself at home, it is necessary to withdraw the material used in the collection in the laboratory or hospital responsible.The maximum time between blood collection and urine sample delivery (or vice versa) is 72 hours.

It is also important to tell the doctor or doctor which medications you take regularly. In some cases, it may be necessary to stop using the medication. However, do not stop taking any medicine without a professional authorization.

How it is done

Urine collection

Creatinine clearance requires urine collection for 24 hours. This means that the person will spend a day urinating exclusively in a plastic jar provided by the laboratory or hospital. This container should be sealed and sent to the hospital or laboratory.

Since a difference of at most 72 hours is required between collection of urine and blood, the patient may be instructed to collect urine the day before of the blood test. In the hospital or laboratory, the creatinine test is performed by a health care professional as follows:

In the hospital or laboratory, the creatinine test is performed by a healthcare professional as follows:

With the patient seated, a rubber band is tied around his arm to stop the flow of blood. This causes the veins to become wider, helping the practitioner hit one of them.

  • The professional cleans the arm area to be penetrated by the needle.
  • The needle is inserted into the vein. This procedure can be done more than once until the health care provider hits the vein and is able to remove the blood.
  • Blood collected in the syringe and placed in a tube
  • The elastic is removed and a gauze is placed on the where the health professional inserted the needle, to prevent any bleeding. He or she can put pressure on the bandage to staunch blood
  • A bandage is placed on the spot.
  • Examination time

The blood test takes a few minutes to complete and may take longer in cases

The urine test requires a full day's collection (24 hours).

Post-examination recommendations

There are no recomendations especially after the examination. The patient can do his / her activities normally. Since it is necessary to fast for at least three hours, the patient may eat after collection.

Frequency of the test

There is no periodicity to perform creatinine clearance. It will depend on the physician's guidelines and the presence or absence of diseases that must be followed up by the examination, such as chronic renal failure.


Risks involved in creatinine clearance are extremely rare. At most, there may be a hematoma at the site where blood was withdrawn. In some cases, the vein may become swollen after the blood sample is collected (phlebitis), but this can be reversed by making a compress several times a day.

People who use anticoagulant medications or have coagulation problems may suffer from a bleeding after collection. In these cases, it is important to inform the health care provider of the problem prior to collection.

Urine collection can be uncomfortable, since the person needs to urinate in the container for a full day. However, there are no risks involved either.


Results are complete within a few days and show mean creatinine clearance. This means that a calculation is made based on blood and urine dosages, showing the amount of creatinine the kidneys are able to filter per minute.

Normal values ​​for creatinine clearance can be made according to the laboratory or hospital .

Normal results

Reference values ​​for creatinine clearance are:

Children: 70 - 140 mL / min / 1.73 m2

  • Any disease or condition that affects the glomeruli may decrease the ability of the patient to function properly, of the kidneys to clear creatinine and other waste from the blood. When this occurs, creatinine clearance is compromised, increasing the levels of the substance present in the blood and reducing the amounts that should be found in the urine.
  • The less effective the renal filtration, the lower the clearance result. A creatinine that is not being properly filtered by the kidneys may indicate some diseases and conditions:
  • Blocked urinary tract

Kidney infection

Kidney failure


  • Muscle disorders such as rhabdomyolysis
  • The creatinine clearance rate may also be lower than normal when there is decreased blood flow to the kidneys. In such cases, the result may indicate problems such as congestive heart failure and acute or chronic renal failure.
  • A high creatinine clearance may occasionally be seen during pregnancy and in people who exercise excessively and / or diets rich in red meat . However, this test is not usually used to monitor these conditions.
  • What may affect the test result?
  • Creatinine clearance rates tend to decline over the years, since kidney capacity to filter the blood.

Certain drugs may decrease creatinine clearance. People who have only one kidney functioning usually have normal clearance rates because the functional kidney will compensate for the lack of the other organ by increasing its rate of filtration.

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