Transcripts
DR. BRANDT:
Now creatinine is the most commonly used measure to estimate the GFR. Creatinine is a by-product of normal muscle metabolism; it has absolutely nothing to do with the kidney itself. However, it is created at a fairly constant rate because your muscle mass is relatively constant. And if your kidneys work well, it's excreted at a relatively constant rate.
Hence, the level of creatinine in the blood (if your muscle mass is stable, and it usually is) is stable and is a good way to estimate how well the kidneys are getting rid of waste products.
It's a good measure of the general function of the kidney.
You can get creatinine tested in any laboratory. It's easy to obtain by a blood test-- easier for some children than others, of course-- but it does overestimate the actual kidney function a little bit. The reason creatinine overestimates GFR is that creatinine is secreted directly into the renal tubules as well as being filtered. It's also somewhat insensitive to small or slow changes in the kidney function in the GFR. But still it is certainly the most easily obtained and useful measure that we have.
