Which in the following when increased can cause a shift of the oxygen-hemoglobin dissociation curve to the left?

**Core Concept**
The oxygen-hemoglobin dissociation curve (ODC) describes the relationship between the partial pressure of oxygen and the saturation of hemoglobin with oxygen. A left shift of the ODC indicates that hemoglobin has a higher affinity for oxygen, making it more difficult for oxygen to be released to tissues.

**Why the Correct Answer is Right**
Increasing 2,3-bisphosphoglycerate (2,3-BPG) levels in red blood cells can cause a right shift of the ODC, not a left shift. This is because 2,3-BPG binds to hemoglobin, reducing its affinity for oxygen and promoting the release of oxygen to tissues. On the other hand, increasing the levels of 2,3-BPG's antagonist, 2,3-diphosphoglycerate (2,3-DPG) does not exist in this list, but it is worth noting that an increase in 2,3-DPG levels would also cause a right shift. However, an increase in 2,3-BPG's antagonist would cause a left shift. The correct answer is an increase in 2,3-DPG's antagonist or a decrease in 2,3-BPG levels or an increase in carbon dioxide (CO2) levels, or an increase in pH, or a decrease in temperature, or 2,3-DPG's similar compound. However, the correct answer is not explicitly listed.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incomplete and does not provide a clear answer.

**Option B:** An increase in 2,3-BPG levels would cause a right shift of the ODC, not a left shift.

**Option C:** An increase in carbon dioxide (CO2) levels would cause a left shift of the ODC, but CO2 is not explicitly listed as an option.

**Option D:** This option is also incomplete and does not provide a clear answer.

**Clinical Pearl / High-Yield Fact**
To remember the factors that cause a left shift of the oxygen-hemoglobin dissociation curve, use the mnemonic "CO2, pH, and temp": carbon dioxide (CO2) levels, pH, and temperature. An increase in CO2 levels, an increase in pH, or a decrease in temperature would cause a left shift of the ODC.

**Correct Answer: C.**