Most nitrogen in the blood resides in proteins, and the amount of nitrogen contained in proteins is high in relation to amino acid content. When proteins are metabolized, the nitrogen-containing components are removed from the amino acids, a process known as deamination. The resulting protein metabolites include urea, creatinine, ammonia, creatine, and uric acid. Levels of these nonprotein nitrogenous compounds reflect various aspects of protein balance and metabolism.