what is creatinine serum
Lots More Information. Creatinine is a chemical molecule in the blood. Its level in the blood is an indicator of how well the kidneys are working. Â© istockphoto /raycat. Creatinine is a chemical molecule that is present in the serum (liquid portion) of the blood.It's produced from another molecule, creatine, which is a component of muscle.ots More Information. Creatinine is a chemical molecule in the blood. Its level in the blood is an indicator of how well the kidneys are working. Â© istockphoto /raycat. Creatinine is a chemical molecule that is present in the serum (liquid portion) of the blood.