What are BUN & creatinine levels?

The Blood Urea Nitrogen (BUN) level is a measurement of the chemical urea in the blood. It is a reflection of the amount of protein breakdown in the blood and it will accumulate with kidney malfunction. Creatinine is a break down product of muscle metabolism and is measured in the blood. It will also accumulate in the blood with kidney malfunction. Measurements of these two chemicals can be used to estimate the glomerular filtration rate (eGFR).