Common Tests

Creatinine (Cr)

Creatinine is a simple blood test that is used to measure how well your kidneys are functioning.

Science Behind This Test

Creatinine is released from the muscle tissue in the body. The creatinine enters the blood stream and is removed from the body by the kidneys. The kidneys are very efficient at getting rid of creatinine and essentially get rid of all of the creatinine that is produced. In a normal situation creatinine is continuously released from the muscle and continuously removed by the kidneys. The level of creatinine in the blood should remain stable.

When the creatinine starts to rise it usually means that the kidneys are not getting rid of it effectively. This can sometimes mean that there is a kidney problem. If your creatinine is elevated it is important to repeat the test. Sometimes creatinine can increase temporarily during times of illness or dehydration and does not reflect kidney problems.

Consider these important points:

  1. Creatinine is released from the muscle. Those with more muscle release more creatinine and their blood levels will be higher. Men have more muscle mass than women and therefore usually have a higher creatinine. Body builders and athletes can also have higher levels of creatinine.
  2. Creatinine can be higher during dehydration. If you are sick and not eating or hydrating properly then creatinine may increase.
  3. Creatinine can be higher in people taking certain medications such as water pills (diuretics) or certain blood pressure medications.
  4. If the creatinine is low it usually means that the muscle mass is low.

Health care professionals use the creatinine to provide an estimate of the glomerular filtration rate (eGFR) which is a calculated measure of kidney function. The estimated glomerular filtration rate is a formula based on the creatinine that takes into account age, gender, and ethnicity.