Which of the following is a general term for diseases affecting blood proteins?

The term "hemoglobinopathy" refers specifically to a group of diseases that are caused by genetic defects in the hemoglobin molecule, which is a vital blood protein responsible for oxygen transport. While it is a specific type of blood protein disorder, it is included here as the correct answer due to its focus on disorders related to blood proteins.

The other options relate to different medical conditions: "gas gangrene" is a type of bacterial infection characterized by tissue death near infected wounds, "fungemia" refers to the presence of fungi in the bloodstream, and "immunodeficiency" is a condition where the immune system's ability to fight infections is compromised, which can be linked to various causes but is not specific to blood proteins. While all options pertain to diseases, only hemoglobinopathy directly involves a category of disorders specifically affecting blood proteins.