Creatinine

What is a creatinine test?

This test measures creatinine levels in a sample of your blood and/or urine (pee). Creatinine is a normal waste product in your body. It’s made when you use your muscles and some of the muscle tissue breaks down.

Normally, your kidneys filter creatinine from your blood and remove it from your body in your urine. If there is a problem with your kidneys, creatinine can build up in your blood and less may be released in urine. If blood and/or urine creatinine levels are not normal, it may be a sign of kidney disease.

Creatinine in blood may be measured by itself or as part of a group of tests called a comprehensive metabolic panel (CMP) or a basic metabolic panel (BMP). Your health care provider may order these tests as part of a routine checkup.

Other names: blood creatinine, serum creatinine, urine creatinine, kidney function, renal function

What is it used for?

A creatinine test is used to help:

• Check the health of your kidneys
• Diagnose kidney disease
• Monitor known kidney problems and see how well treatment is working
• Check for side effects from medicines that may affect your kidneys

Creatinine testing alone isn’t the best way to check how well your kidneys are working. That’s because people make different amounts creatinine depending on how much muscle they have, the foods they eat, their age, and how active they are. So, the results from creatinine testing are often used in calculations or compared with other substances to help get more information:

• Creatinine levels in blood are often used to calculate how fast your kidneys filter waste out of your blood. This is called an estimated glomerular filtration rate (eGFR). The calculation includes information about your age, weight, height, and sex. An eGFR is a more accurate way to measure kidney health than creatinine levels in blood or urine alone. An eGFR can also help show how serious kidney disease may be.
• Creatinine levels in blood and urine maybe be compared with each other. This is called a creatinine clearance calculation. Like an eGFR, it estimates how fast your kidneys filter waste. But an eGFR is more accurate. A creatinine clearance may still be useful to help identify the cause of high or low levels of blood creatinine in people who have very high muscle mass or a loss of muscle mass from age, illness, or the loss of an arm and/or leg.
• Creatinine levels in urine may be used to calculate a urine albumin to creatinine ratio (UACR), which is sometimes called a microalbumin creatinine ratio. Albumin is the main protein found in blood. Normally your kidneys filter out just a trace of albumin, or none at all. If larger amounts of albumin pass into your urine, it may be a sign of kidney damage. A UACR compares the amounts of creatinine and albumin in your urine to get a more accurate measurement of how much albumin is in your urine.
• Creatinine blood levels measured as part of a CMP or a BMP may be compared with the level of BUN (blood urea nitrogen) that’s measured in the same test. This can help find out the cause of a kidney problem.