Why does anemia cause fatigue and dyspnea?

• A. Increased tissue oxygenation.
• B. Increased red blood cell production.
• C. Decreased cardiac output.
• D. Decreased tissue oxygenation.

Answer: (D)

Anemia reduces the blood’s oxygen-carrying capacity, so tissues end up receiving less oxygen than they need. Oxygen delivery to tissues depends on how much oxygen is carried in the blood; with fewer red blood cells or less hemoglobin, arterial oxygen content drops, and less oxygen reaches cells even if breathing seems normal. Without enough oxygen for energy production, cells fatigue quickly and muscles tire, contributing to overall fatigue. The body tries to compensate by increasing heart rate and breathing to deliver more oxygen, which can cause shortness of breath with exertion. These compensatory efforts help but may not fully restore tissue oxygenation, so fatigue and dyspnea persist.

Increasing tissue oxygenation would lessen these symptoms, while increased red blood cell production is a corrective response to anemia rather than a cause of the symptoms, and decreased cardiac output isn’t the typical driver in the common presentation of anemia. The link to fatigue and dyspnea is best explained by decreased tissue oxygenation.