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 by-product 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.

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. 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.

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 millilitres of blood per minute (mL/min).

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.