What is Creatinine Clearance 6 hrs, Urine?

Also Known As: CCT, CrCl

A creatinine clearance test uses both a blood and urine sample in order to see how well the kidneys are functioning.

Creatinine is created as a waste byproduct of normal muscle activity. The kidneys remove creatinine from the blood and allow it to be eliminated from the body in the urine.

A creatinine clearance test compares the amount of creatinine in the blood and urine. This comparison provides information about how well the kidneys are filtering the blood and can be important for detecting and monitoring kidney problems.

The purpose of a creatinine clearance test is to assess kidney function. In particular, creatinine clearance is used to determine the estimated glomerular filtration rate (eGFR), which describes how well the kidneys are filtering the blood.

Measuring creatinine clearance to evaluate kidney filtration may be done for many different reasons. It can be an important tool for the diagnosis, screening, and monitoring of kidney disease.

Testing that happens after symptoms have occurred is part of making a diagnosis. Testing before symptoms have appeared is known as screening. Testing to observe or follow a condition is monitoring.

Diagnosis

A creatinine clearance test may be part of the diagnostic process if you have symptoms that are consistent with a possible kidney problem such as urinary changes, itching, loss of appetite, and swollen feet. Creatinine clearance testing may also help diagnose whether kidney problems are present in people with more general symptoms like fatigue.

Screening

Some people are at higher risk of kidney problems, including people with diabetes, high blood pressure, or a family history of kidney disease. For these patients, kidney function tests may be done as screening in order to try to detect kidney problems before any symptoms have occurred.

In many cases, initial screening is done with a creatinine blood test. Specialized formulas have been established to estimate the glomerular filtration rate based solely on blood levels of creatinine. A creatinine blood test is easier to conduct because it does not require a urine sample. However, a creatinine clearance test that includes a urine sample may be used if the blood test alone has an abnormal result or if individual patient factors make the blood creatinine measurement less reliable.

Monitoring

Creatinine clearance tests can be used to observe how kidney function changes over time. This type of monitoring may be useful in multiple situations:

• After kidney disease has been diagnosed, testing can help track how the disease progresses.
• Testing before and after treatment for kidney disease can assess how well the treatment is working.
• When a drug or treatment with side effects that can affect kidney function is prescribed, a creatinine clearance test can check for possible kidney damage or abnormal kidney function.

What does the test measure?

A creatinine clearance test measures the amount of creatinine in a sample of blood taken from your arm and in a sample of all the urine you produce during a 24-hour period.

Creatinine develops as a result of the breakdown of creatine, a chemical that helps provide the muscles with energy. The body consistently produces creatinine as a byproduct of normal activity, and the tiny filters in the kidneys, called glomeruli, work to remove the creatinine from the blood. Creatinine then can be carried out of the body in the urine.

A creatinine clearance test helps show how well this process is working by measuring the amount of creatinine in both the blood and urine. By applying a specific formula, these blood and urine measurements can estimate the amount of blood being filtered by the glomeruli in the kidneys, which is the glomerular filtration rate (GFR).

To calculate creatinine clearance, the creatinine level in the urine is multiplied by the total volume of urine produced over 24 hours. This is then divided by the amount of creatinine in the blood. The final value is converted to milliliters of blood per minute (mL/min).

Online calculators are available to apply this formula and determine creatinine clearance. These calculators often include adjustments to account for the fact that creatinine levels are affected by body size. The final unit of measurement for creatinine is typically milliliters per minute per 1.73 square meters of body surface area (mL/min/1.73 m2).

When should I get a creatinine clearance test?

Like other kidney function tests, creatinine clearance may be measured if you are showing signs of possible kidney impairment. In these cases, it is a type of diagnostic test that can help to identify the cause of your symptoms.

Creatinine clearance may be tested if you are at risk of having kidney problems. For example, people who are going to start using medications that affect the kidneys may take this test. In addition, testing can be done to try to find kidney disease earlier in people with diabetes, high blood pressure, or a family history of kidney disease.

Other types of kidney function tests can be used in many of these situations, but creatinine clearance may be suggested if you have a diet that is very high or low in protein or if you have either very little or a lot of muscle mass. For people with these individual factors, a creatinine clearance test is usually more accurate than a test of creatinine in your blood alone.

Creatinine clearance can be used as a follow-up test if another type of kidney function test shows an abnormal result. In these cases, the combination of creatinine measurement in both blood and urine offers a method to confirm the findings of the initial test.

How to get tested

A creatinine clearance test is normally prescribed by a doctor. The blood sample is taken in a laboratory, hospital, or medical office. The urine sample requires collecting all of your urine during a 24-hour period, so at least part of this sample collection is often done at home. Both the blood and urine samples are analyzed by a lab to measure creatinine and calculate the creatinine clearance.

Can I take the test at home?

Limited or no options are available for at-home test kits of creatinine clearance.
Some at-home test kits measure creatinine in either the blood or the urine alone, but a full creatinine clearance test is generally not offered in commercial at-home tests.

With a standard creatinine clearance test, much of the urine sample is taken at home because the test requires that you collect all your urine for a full 24 hours.