A patient with anemia is found to have a high level of serum erythropoietin and a low reticulocyte count. What is the most likely diagnosis?

The combination of high serum erythropoietin and low reticulocyte count suggests a problem with the production of red blood cells, rather than a lack of stimulation. Pure red cell aplasia is a condition characterized by a selective failure of erythropoiesis, leading to anemia and low reticulocyte count despite high levels of erythropoietin.