An increase in which of the following increases the O2 affinity of hemoglobin?: (A) Temperature, (B) PCO2, (C) H+ concentration, (D) Carbon monoxide added to the blood
Answer is D. A small amount of carbon monoxide added to blood increases its oxygen affinity, that is, it causes a leftward shift of the O2 dissociation curve . All the other choices reduce the oxygen affinity of hemoglobin, that is, they shift the dissociation curve to the right.