Fatigue is the most common presenting symptom of anemia because reduced hemoglobin levels impair oxygen delivery to tissues, leading to decreased energy production at the cellular level. This oxygen deficit affects muscle and organ function, causing patients to feel tired and weak. Other symptoms may occur, but fatigue directly reflects the physiological impact of anemia on oxygen transport and cellular metabolism. Prompt recognition of fatigue in anemia is crucial for early diagnosis and management.

Reference: Harrison's Principles of Internal Medicine, Jameson et al., 20th Edition.