Creatinine is a breakdown product of muscle that is usually produced at a
fairly constant rate by the body (depending on your muscle mass). It is
filtered by the kidney. If the filtering of the
kidney is deficient blood
levels rise. This effect is used as an indicator of
renal function.
Creatinine is a simple test and it is the most commonly used indicator of renal
function. It should be remembered that rise in blood creatinine levels is
observed only with marked damage to functioning nephrons; therefore this test
is not suitable for detecting early kidney disease. A much better estimation
of kidney function gives the
creatinine clearance test[?].