Which statement about COHb levels is true?

Which statement about COHb levels is true?

• A. Normal COHb levels are 0-1 %
• B. COHb levels in smokers are 0-1 %
• C. COHb levels never exceed 5 %
• D. COHb levels are unaffected by smoking

Answer: (A)

Carboxyhemoglobin forms when carbon monoxide binds to hemoglobin, reducing the blood’s oxygen-carrying capacity. In healthy nonsmokers, COHb is typically 0–1%. Smoking exposes the lungs to CO, raising COHb to higher levels—often several percent—so the idea that smokers have 0–1% is not correct. COHb levels can exceed 5% with exposure, and smoking does affect COHb, so a statement that they are unchanged is false. Thus, the true statement is that normal COHb levels are 0–1%.

Carboxyhemoglobin forms when carbon monoxide binds to hemoglobin, reducing the blood’s oxygen-carrying capacity. In healthy nonsmokers, COHb is typically 0–1%. Smoking exposes the lungs to CO, raising COHb to higher levels—often several percent—so the idea that smokers have 0–1% is not correct. COHb levels can exceed 5% with exposure, and smoking does affect COHb, so a statement that they are unchanged is false. Thus, the true statement is that normal COHb levels are 0–1%.