A previously healthy elderly man shows signs of weakness and fatigue. What is the most likely cause if laboratory findings indicate microcytic anemia?

• A. Chronic myelogenous leukemia
• B. Aplastic anemia
• C. Gastrointestinal blood loss
• D. Vitamin B12 deficiency

Answer: (C)

Microcytic anemia is characterized by red blood cells that are smaller than normal and is commonly associated with conditions where iron deficiency plays a central role. In the case of an elderly patient showing signs of weakness and fatigue along with laboratory findings indicating microcytic anemia, gastrointestinal blood loss is a highly plausible cause.

Bleeding in the gastrointestinal tract can stem from various sources, including ulcers, polyps, diverticula, and malignancies, particularly in older adults. Such chronic blood loss leads to a depletion of iron stores, resulting in microcytic anemia due to insufficient iron being available for hemoglobin synthesis in red blood cells.

The other potential causes of anemia listed do not typically result in microcytic anemia. For instance, chronic myelogenous leukemia usually presents with a different type of anemia due to bone marrow involvement rather than iron deficiency. Aplastic anemia leads to a decrease in all types of blood cells due to bone marrow failure and does not cause microcytic anemia specifically. Lastly, vitamin B12 deficiency results in macrocytic anemia, characterized by larger than normal red blood cells due to impaired DNA synthesis, thus is not compatible with the presentation of microcytic anemia.

Considering the patient’s age and the laboratory findings, gastrointestinal blood loss is