A patient presents with shortness of breath during mild activity, along with multiple petechiae and spontaneous bleeding. His red blood cell count is below 100,000/mm³, and both hematocrit and hemoglobin levels are decreased. What is the most likely diagnosis?

Explanation

The patient's symptoms of dyspnea on minimal exertion, petechiae, spontaneous hemorrhages, and severe pancytopenia (RBC count under 100,000/mm³) along with low hematocrit and hemoglobin strongly indicate aplastic anemia. Pernicious anemia, thalassemia, and sprue typically present differently and do not cause such profound pancytopenia.