**Question:** Oxygen affinity is increased by all of the following except

A. Decreased pH
B. Increased 2,3-diphosphoglycerate (2,3-DPG)
C. Increased partial pressure of oxygen (pO2)
D. Increased temperature

**Core Concept:** Oxygen affinity refers to the ability of a molecule to bind to a specific site on a protein, in this case, the oxygen-binding site in hemoglobin. Oxygen affinity can be influenced by various factors, including pH, 2,3-DPG, pO2, and temperature.

**Why the Correct Answer is Right:** Increasing pH generally lowers oxygen affinity in red blood cells, as it causes a conformational change in hemoglobin that weakens its binding to oxygen. In contrast, increased 2,3-DPG and pO2 increase oxygen affinity by stabilizing the oxygen-bound form of hemoglobin. Higher temperature generally increases oxygen affinity due to the increased kinetic energy, which weakens the interaction between oxygen and hemoglobin.

**Why Each Wrong Option is Incorrect:**

A. Decreased pH: This decreases oxygen affinity by causing a conformational change in hemoglobin, favoring the deoxygenated form.
B. Decreased pH: This decreases oxygen affinity by causing a conformational change in hemoglobin, favoring the deoxygenated form.
C. Increased partial pressure of oxygen: This increases oxygen affinity by reducing the partial pressure gradient between the tissues and the blood, favoring oxygen binding to hemoglobin.
D. Increased temperature: This increases oxygen affinity by increasing the kinetic energy, favoring the oxygen-bound form of hemoglobin.

**Clinical Pearl:** Understanding oxygen affinity and its modulators is essential for physicians to accurately assess patients' respiratory status, particularly in critical care and high-altitude medicine. A decreased pH (acidosis) can lead to a false increase in oxygen saturation, which may delay the initiation of effective respiratory support. In contrast, increased pH (alkalosis) may lead to a false decrease in oxygen saturation, potentially causing inadequate respiratory management.

**Explanation:**

Oxygen affinity can be influenced by various factors. In this multiple-choice question, we are discussing the impact of pH, 2,3-DPG, partial pressure of oxygen (pO2), and temperature on oxygen affinity.

1. Decreased pH (acidosis): A low pH leads to a conformational change in hemoglobin, favoring the deoxygenated form and decreasing oxygen affinity.
2. Increased 2,3-DPG: This is a natural product of glycolysis that binds to hemoglobin, stabilizing the oxygen-bound form and increasing oxygen affinity.
3. Increased partial pressure of oxygen (pO2): A low pO2 favors oxygen binding to hemoglobin, increasing oxygen affinity.
4. Increased temperature: Higher temperatures increase kinetic energy, favoring the oxygen-bound form of hemoglobin and increasing oxygen affinity.

In summary, option D (increased temperature) is correct as it increases oxygen affinity due to increased kinetic energy, favoring the oxygen-bound form of hemoglobin.