What is Serum Creatinine?

Serum creatinine is the concentration of a compound known as creatinine in the blood or urine. It is tested during routine metabolic panels, usually with the goal of evaluating a patient who may be at risk for kidney disease. Most labs have the ability to check serum creatinine, often providing same day turnaround service with rapid results.

The serum creatinine test can be recommended as part of a comprehensive panel of a patient or as a standalone test because there are specific concerns. When a doctor recommends this diagnostic test, patients may want to ask why it is being recommended, what the possible results are, and how long it will take to receive results.

Creatinine is a waste product produced by the body at a relatively stable rate. It is a byproduct of the cycle used to deliver energy to the muscles. The kidneys are responsible for clearing creatinine from the body and when they are not functioning properly, more of this compound starts to circulate in the blood. In the early stages of a kidney problem the levels may be within normal range, but eventually they will rise high enough to indicate that the kidneys are not working.

People can also have high serum creatinine in pregnancy or in the wake of a muscle injury in some cases. Patients with high test results may be evaluated to rule out these possibilities. A doctor would expect to see high levels in patients with kidney failure, kidney cancers, and diseases of the cardiovascular system.

This test is relatively low cost, making it appealing to a doctor who wants to work a patient up quickly to rule out possibilities without expending a lot of money or exposing the patient to invasive tests. Once serum creatinine is determined, a lab technician can use the information to generate a creatinine clearance value, taking the patient's age, height, weight, and gender into account. This value can provide even more information about kidney function.

One problem with the serum creatinine test is that people can be experiencing kidney disease and the start of kidney damage while the values still fall within normal range. Other values on a metabolic panel can provide additional information about kidney function. Once the kidneys start to function abnormally, it is common to see other changes in a blood profile because the kidneys are not able to express a wide variety of waste products.