The differential diagnosis of anemia in admitted patients encompasses a large number of conditions, and the initial work up should include a thoughtful clinical history and physical examination and several tests to investigate vitamin and/or iron deficiency, liver and kidney diseases, infections, hemoglobinopathies, cancers, drugs, autoimmune and hematologic diseases, etc. AIHA should be suspected in patients presenting with macrocytic anemia of various degree and altered hemolytic markers: increased LDH and unconjugated bilirubin, decreased haptoglobin, and augmented absolute reticulocytes. This evidence concerns the gene HP and infection.