Which substance increases in the blood as a result of cigarette smoke exposure?

• A. Carbon monoxide
• B. Ammonia
• C. BUN
• D. Creatinine

Answer: (A)

Cigarette smoke introduces carbon monoxide into the bloodstream. Carbon monoxide binds strongly to hemoglobin to form carboxyhemoglobin, which greatly raises its level in blood and reduces the blood’s capacity to carry and release oxygen to tissues. This is the direct and characteristic blood change from smoke exposure. Ammonia, BUN, and creatinine are not specifically increased by smoking: ammonia relates more to liver or kidney function and metabolic state, while BUN and creatinine reflect renal function rather than a direct effect of inhaled smoke. So the substance that increases in blood after cigarette smoke exposure is carbon monoxide.