Creatinine, Serum

The creatinine blood test is used to assess the functioning of kidneys. Creatinine blood test is done either alone or along with BUN (blood urea nitrogen) test, or as part of Comprehensive renal function test. This test is done as a routine screening test in healthy people. Creatinine is a nitrogenous waste product produced by muscles from creatine. Creatinine is majorly filtered from the blood by the kidneys and released into the urine, so serum creatinine levels are usually a good indicator of kidney function. Serum creatinine is more specific and more sensitive indicator of renal function as compared to BUN because it is produced from muscle at a constant rate and its level in blood is not affected by protein catabolism or other exogenous products. It is also not reabsorbed and very little is secreted by tubules making it a reliable marker. Serum creatinine levels are increased in pre renal, renal and post renal azotemia, active acromegaly and gigantism. Decreased serum creatinine levels are seen in pregnancy and increasing age.

1. Will exercise affect creatinine levels?

Excess excercise may slightly increase the levels of serum creatinine, but not to the abnormal levels, due to building of muscle mass.

2. Does diet affect creatinine levels?

Eating cooked meat prior to testing can increase the level of creatinine temporarily.

3. What is creatine? Can dietary creatine increase creatinine levels?

Creatine is synthesised in the liver and transported to muscles, where it is used as a source of energy for muscle activity. In the muscle, some of the creatine is spontaneously converted to creatinine. As the levels of both creatine and creatinine depend on muscle mass, men usually have higher levels than women. Creatine is now available as a dietary supplement, which can increase the serum creatinine levels.

4. Can age change creatinine levels?

Creatinine levels relate to both muscle mass and to kidney function. As age increases, muscle mass decreases but kidneys tend to function less effectively, so there is not much change in the net creatinine levels in the blood.

5. What is a BUN/Creatinine ratio?

The normal BUN/creatinine ratio is usually between 10:1 and 20:1. It increases due to decreased flow of blood to the kidneys (in conditions such as congestive heart failure or dehydration), gastrointestinal bleeding, or increased protein in the diet. It is decreased in liver disease and malnutrition.