Serum Creatinine which is also known as creatinine blood test is done to measure the creatinine levels in the blood. Creatinine is the waste product in the body which is formed when creatine breaks down. Creatine is mainly found in your muscles and a serum creatinine will help your doctor know how well your kidneys are working. If high levels of creatinine are found in the body then that can mean your kidneys are either damaged or not working properly. Serum creatinine is done along with a few other lab tests like BUN and BMP.