Creatinine Clearance Exam: what it is for and results

What is creatinine clearance?

Creatinine clearance is an exam done to assess kidney function. It does this by comparing the amount of creatinine in the blood and urine. The kidneys serve to filter the blood and among other substances eliminate the extra creatinine in it.

Creatinine is a substance naturally produced by the muscles and eliminated by the kidneys. If the values ​​are changed, it may mean that the kidney function is altered.

Creatinine

It is a substance produced by the muscles from creatine , a compound of amino acids. The more muscle mass a person has, the greater the amount of creatine in their body and the more creatinine is produced.

This substance is used as a marker. If creatinine is elevated in the blood, it means that the kidneys are unable to filter it effectively. If creatinine is not being filtered, it is likely that other substances, such as toxins, are also accumulating in the blood.

Excess creatinine in the blood is a sign that the kidneys may be working poorly.

Symptoms of excess creatinine

Although the substance is not dangerous, its excess can cause some symptoms. Are they:

  • Tiredness;
  • Lack of air;
  • Swelling of the legs or arms;
  • Frequent confusion;
  • Nausea and vomiting.

What is creatinine clearance for?

The creatinine clearance test serves to assess the functionality of the kidneys. Creatinine is a substance produced by the body that the kidneys eliminate all the time.

The comparison between blood and urine creatinine may indicate kidney problems. The results are excesses of the substance. If there is too little creatinine in the urine and too much in the blood, the kidneys may not be able to do their job, causing an accumulation of creatinine and other materials that should be filtered by the kidneys.

This test is able to detect kidney failure at an early stage.

How is the creatinine clearance test done?

The procedures for examining creatinine clearance are as follows:

Urine collection

Urine collection must be done within 24 hours. A container is provided where the patient must urinate during this time and, at the end, it must be closed and taken to the laboratory or hospital.

In the case of women, it is recommended that urine collection is not performed during the menstrual period.

Blood collection

Blood collection is carried out at the hospital or laboratory. It needs to be carried out with a maximum of 72 hours difference in the collection of urine, so it is common to be carried out at the beginning or at the end of the material collection process.

The patient, seated, has a tourniquet (latex or elastic tube) tied to the arm to interrupt the flow of blood, allowing the veins to be more visible to the professional who will perform the collection.

A needle is inserted into the vein (this procedure can be repeated if the professional is unable to hit the vein on the first attempt) and the blood is drawn by a syringe and deposited in a tube.

After that, the needle is removed and a bandage is made to stop the bleeding. The material is then sent to the laboratory with the urine.

Exam

In the laboratory, the amount of creatinine in the blood and urine is measured. The values ​​are placed in a formula that takes into account the patient’s weight, age and biological sex. The values ​​resulting from the formula are the results, which come out in a few days after the collection has been carried out.

When should the exam be done?

The creatinine clearance test should be performed at the request of the doctor, who decides whether it will be necessary. Some indications are:

Family history of kidney disease

Kidney disease can be genetic, so if you have someone in the family with this type of disease, the test is recommended from time to time to monitor the condition of the kidneys.

Disease patients who can cause kidney problems

Some conditions can pose risks to the kidney system. Among them are diabetes , hypertension, obesity , urinary tract infections, gout , people with high uric acid, polycystic kidneys, among others. The test is recommended in these cases to prevent kidney disease.

Use of drugs that alter kidney function

Several drugs are filtered through the kidneys and can alter kidney function. It is necessary to monitor patients taking this type of medication. Your doctor will inform you when prescribing a medication that may alter your kidney function.

Smokers

Smoking can cause dysfunctions in all organs of the body. Smokers should always be aware of their health status, and tests such as creatinine clearance should be included in this attention.

Over 50 years old

With age, the organs may begin to show flaws. Routine examinations to monitor the functioning of the kidneys can be indicated above 50 years of age.

Contraindications to the creatinine clearance test?

The creatinine clearance test involves only removing a small amount of blood and collecting urine, so there are no contraindications.

Pre-examination and post-examination care

Because it is an extremely simple exam, little care is needed.

Pre-exam

Meat

It is recommended to avoid eating meat during the previous day and during urine collection, as the meat changes the amount of creatinine in the blood.

Fast

Some types of blood tests require fasting, but not all laboratories require it for the creatinine test. When requested, it should be around 3 to 8 hours before blood is drawn.

Post-examination

Movements

After drawing blood, it is recommended that you do not use force or move the arm from which the blood was removed during the rest of the day to avoid bleeding.

Comer

In cases where fasting is required for the blood test, a light diet is recommended right after the blood is drawn.

Results of the creatinine clearance test

The test results will indicate whether there is a change in the amount of creatinine in your blood. Any change in the kidney’s functionality can reduce its ability to filter and other functions it performs.

If there is a deficiency in the filtration of the kidneys, creatinine accumulates in the blood and appears in the urine. This also happens with other substances that should be filtered out by the kidneys and this can cause serious problems.

When kidney function is decreased, the result is less than the reference values ​​and when it is increased, the value goes up. This is because the test does not measure the amount of creatinine in the blood, but the amount of creatinine filtered by the kidneys.

Reference values

These are the expected results of the exam. If your creatinine clearance test is within these values, he is healthy. The measurement shows the amount of creatinine that is filtered out by the kidneys per minute.

  • Men: 85 – 125 mL / min / 1.73 mL;
  • Women: 75 – 115 mL / min / 1.73 m²;
  • Children: 70 – 140 mL / min / 1.73 m².

What can affect the results?

Reduced kidney function

Reduced kidney function indicates kidney failure and will cause the results to be below the reference values. The condition needs to be treated, as inefficient kidneys cannot filter the blood and toxic substances build up in it.

Exercises

Exercises increase the values ​​of filtered creatinine per minute in the kidneys.

Meat

Meat increases the amount of creatinine in the blood.

Medicines

Certain medications can alter kidney function, which appears in the creatinine clearance test, and can appear as an excess of the substance in the urine or blood. Your doctor can tell you what these medications are and, if you take any of them, this will be taken into account during the exam.

Depending on the type of medication, it may be necessary to suspend its use for the test. For example hydantoin, ascorbic acid  and trimethoprim are drugs that can cause problems with urination. However, only the doctor can indicate this and you should not stop using medications on your own.

Attention!

NEVER  self-medicate or stop using a medication without first consulting a doctor. Only he will be able to tell which medication, dosage and duration of treatment is the most suitable for his specific case. The information contained in this website is only intended to inform, not in any way intended to replace the guidance of a specialist or serve as a recommendation for any type of treatment. Always follow the instructions on the package insert and, if symptoms persist, seek medical or pharmaceutical advice.

Can pregnant women take a creatinine clearance test?

There is no contraindication for pregnant women to take the test, but pregnancy must be taken into account for the results, as they will be changed. Pregnancy increases the speed of filtration of the kidneys, but this is a fact known to doctors.

Knowing that the pregnancy exists, she enters the account and the results considered normal change, becoming slightly above normal.

This test is not usually required for pregnant women, but it can occur if the woman has a kidney disease already diagnosed.

Risks of the creatinine clearance test

The greatest risk that exists in the creatinine clearance exam is the professional collecting the blood, err the vein many times or crossing it with the needle unintentionally, which is quite annoying, but it is not dangerous.

It is important that, if there are clotting problems or if anticoagulant medications are used, the doctor is advised, as continuous bleeding after collection is possible.

There are no risks related to the creatinine clearance test.

Common questions

Why should urine be collected over 24 hours?

Urine collection takes place over the course of an entire day because the amount of creatinine in it varies according to the time of day due to food and other factors. An average amount of creatinine in the urine over an entire day is required for the test to be accurate.

For this, the first urine of the day must be ignored, its time must be noted and, from that moment, all urine made in the next 24 hours must be collected in the same bottle.


The creatinine test is performed to identify the possibility of early kidney failure. It is an important exam that can be done easily. Share this text with your friends to let them know more about this exam.

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