Which test measures a waste product from protein metabolism and is excreted by the kidneys?

• A. Creatinine
• B. Potassium
• C. Blood Urea Nitrogen
• D. Chloride

Answer: (C)

Protein metabolism leaves urea as a waste product, which the liver makes and the kidneys excrete. A test that measures the amount of urea nitrogen in the blood directly reflects this waste product and how well the kidneys are clearing it. That’s why this test is used to assess both protein metabolism burden and kidney function, with higher levels suggesting reduced renal clearance, dehydration, high protein intake, or increased protein breakdown. Creatinine also relates to kidney function but comes from muscle metabolism rather than protein breakdown in the liver–so it isn’t the direct measure of a protein-metabolism waste product. Potassium and chloride are electrolytes, not waste products from protein metabolism.