Aplastic anemia is caused by a variety of reasons leading to bone marrow hematopoietic failure. So, what is the main diagnostic basis for diagnosing aplastic anemia? It is primarily the bone marrow examination, which shows decreased or severely decreased proliferation at least in one site, such as active proliferation, significant reduction in megakaryocytes, and an increase in non-hematopoietic cells in the bone marrow's granular components. Additionally, there can be a decrease in total blood cells, white cells, red cells, etc., and a reduction in the absolute value of reticulocytes.