Your kidneys filter creatinine, a byproduct of the energy producing acid creatine, out of your blood and into your urine. So by measuring the creatinine levels, whether from the blood or urine, in a laboratory test, a physician can determine the general health of a patient's kidneys based on the filtration rates. In children, the normal level of creatinine in the blood is proportional to their size, but is generally in the range of 0.2 to 1.0 mg/dL.
Significance
Creatinine is a non-protein molecule that is created when your body breaks down creatine, a component of muscle. Creatine is constantly broken down and processed in your body, so a constant supply of creatinine is made. Since creatinine is an end product of creatine metabolism, it needs to be excreted from the body in urine. Your kidneys are responsible for filtering creatinine out of your blood and into your urine.
Normal Levels
Creatinine can be measured in either blood or urine, and in patients with severe kidney problems, both may be measured. Since creatinine is produced from muscle metabolism, the amount made and excreted is directly proportional to muscle mass. Since children are smaller than adults, they tend to have lower blood creatinine levels, which typically range from 0.2 to 1.0 mg/dL of blood. As a child grows larger, creatinine levels should increase until they reach adult levels.
Testing
Blood creatinine is measured from a standard blood draw in your doctor's office. Since it can be a part of a series of blood tests, this is the measurement that is often taken. If your physician feels that more information will be helpful, she may order a test for creatinine level in urine. This test requires a 24-hour urine collection from the patient, making it moderately more cumbersome than the blood draw.
Considerations
If a child's creatinine level is abnormally high or low, it can be an indication of kidney dysfunction. According to MedLine Plus, high levels of creatinine can indicate acute kidney failure or infection, among other disorders, and lower than normal levels may result from disorders such as myasthenia gravis or muscular dystrophy.
Warning
Creatinine levels are not the only indicator of proper kidney function, and it is unlikely that your physician will make a decision based solely on this test. For children with kidney disorders, creatinine along with these other tests will be used to monitor overall kidney health. It is also important to note that your child's baseline creatinine levels may be outside the normal range, but kidney function could be found normal after follow up testing.
