Final answer:
Anemia of chronic disease is the most common microcytic anemia after iron deficiency anemia, especially prevalent among hospitalized patients without blood loss, owing to its association with chronic illnesses that affect erythropoietin production and iron usage.
Step-by-step explanation:
The most common microcytic anemia other than iron deficiency anemia (IDA) and that accounts for more than one-third of anemia in hospitalized patients without blood loss is anemia of chronic disease (ACD). Microcytic anemias result from disorders that affect red blood cell (RBC) production. While conditions like sickle cell anemia, thalassemia, and vitamin deficiency anemia can lead to microcytic anemia, ACD is particularly prevalent amongst the hospitalized patient population, often associated with chronic conditions such as kidney disease, cancer, lupus, and rheumatoid arthritis which can impair erythropoietin production and iron metabolism.