What condition is characterized by a below normal concentration of gamma globulin in the blood?

Hypogammaglobulinemia is the correct choice as it specifically refers to a condition where there is a reduced level of gamma globulin in the blood. Gamma globulins are a class of globulins which include antibodies, and their low concentration can lead to increased susceptibility to infections due to the body’s diminished ability to respond to pathogens.

In this context, understanding the implications of low gamma globulin levels is crucial. Individuals with hypogammaglobulinemia may experience recurrent infections as their immune system is less equipped to fight off illnesses. This condition can be caused by various factors, including genetic mutations, certain diseases, and side effects of treatments such as chemotherapy.

To differentiate it from the other conditions, hypergammaglobulinemia refers to an elevated level of gamma globulins in the blood, indicating an immune response or inflammation, whereas agammaglobulinemia represents the absence of gamma globulins altogether. Normogammaglobulinemia indicates that gamma globulin levels are within the normal range, showing that the immune function is likely adequate.