A 45-year-old man with a history of recurrent upper respiratory tract infections and chronic diarrhea is found to have low IgA levels on blood tests. What is the most likely diagnosis? A) HIV/AIDS B) Common variable immunodeficiency (CVID) C) X-linked agammaglobulinemia D) Chronic granulomatous disease E) Selective IgA deficiency Correct Answer: E) Selective IgA deficiency Explanation: Selective IgA deficiency is a common immunodeficiency disorder characterized by low IgA levels in the blood. Patients often present with recurrent respiratory infections and gastrointestinal issues (e.g., chronic diarrhea). HIV/AIDS (A) presents with opportunistic infections and low CD4 count, not just low IgA. Common variable immunodeficiency (CVID) (B) typically presents with low levels of multiple immunoglobulins, including IgG, IgA, and IgM, and often with recurrent infections. X-linked agammaglobulinemia (C) presents with very low or absent immunoglobulins and severe bacterial infections, usually seen in male children. Chronic granulomatous disease (D) presents with recurrent bacterial and fungal infections, but it is caused by a defect in phagocyte function rather than low IgA. Key Tips for PLAB 1: ✅ Low IgA levels with recurrent respiratory and GI infections = Selective IgA deficiency ✅ Often asymptomatic, but infections can be managed with antibiotics.
