This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Blood, Subject name: Medicine
Which of the following is the most likely effect of increased levels of red blood cell 2,3 diphosphoglycerate (2,3-DPG)? 
Select and explain. 
A. hemolytic anemia due to sulfa drugs, B. increased oxygen affinity, C. decreased oxygen affinity, D. loss of red cell energy
C: decreased oxygen affinity
Answer: C: decreased oxygen affinity 
Explanation: The 2,3-bisphosphoglycerate (2,3-BPG) binds to the central cavity of the heme molecule and changes the configuration in favor of oxygen release. The other common factors that affect oxygen affinity are temperature and pH. The oxygen affinity of Hb is easily characterized by P50; the oxygen tension at which Hb is half-saturated.