Which term refers to a disease that affects hemoglobin within red blood cells?

The term that accurately refers to a disease affecting hemoglobin within red blood cells is Hemoglobinopathy. This term encompasses a group of disorders that result from abnormalities in the hemoglobin molecule itself. Such conditions can lead to various clinical manifestations, including anemia and altered oxygen transport.

Hemoglobinopathies typically arise from genetic mutations that alter the structure or synthesis of hemoglobin, resulting in diseases like sickle cell disease and thalassemia. In contrast, other options like gas gangrene involve bacterial infections leading to tissue necrosis and are not related to hemoglobin. Hodgkin's disease refers to a type of lymphoma affecting the lymphatic system, and immunodeficiency involves disorders that impair the immune response, neither of which pertain to hemoglobin or its function in red blood cells. Thus, Hemoglobinopathy is the specific and correct term that describes diseases affecting hemoglobin directly.