The Test Sample
What is being tested?
This test measures the amount of creatinine in your blood and/or urine. Creatinine is a waste product produced in your muscles from the breakdown of a compound called creatine. Creatine is part of the cycle that produces energy needed to contract your muscles. Both creatine and creatinine are produced by the body at a relatively constant rate. Almost all creatinine is excreted by the kidneys, so blood levels are a good measure of how well your kidneys are working. The quantity produced depends on the size of the person and their muscle mass. For this reason, creatinine concentrations will be slightly higher in men than in women and children.
Results from a blood creatinine test and a 24-hour urine creatinine test may be used to calculate creatinine clearance.
How is the sample collected for testing?
A blood sample is taken from a vein in the arm. You may be asked to collect a complete 24-hour urine sample in addition to having your blood taken (see "Creatinine Clearance"). Your doctor or the laboratory will give you a large container and instructions for properly collecting this sample. You will normally be asked to collect urine as soon as you wake up in the morning until the same time the following day.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.