Basic concepts of AHG testing include which of the following?

• A. AHG is used to detect incomplete antibodies
• B. AHG is used to detect complete antibodies
• C. AHG cannot detect in vivo sensitization
• D. AHG cannot detect in vitro sensitization

Answer: (A)

The main idea is that AHG testing reveals antibodies that have attached to red blood cells in a way that isn’t visible without the antiglobulin reagent. These are typically IgG antibodies, often labeled as incomplete because they don’t cause visible agglutination on their own in saline. The antiglobulin reagent binds to the Fc region of these IgG antibodies on the red cell surface and cross-links them, making agglutination visible. That’s why AHG testing is used specifically to detect incomplete antibodies.

In contrast, complete antibodies (usually IgM) react at immediate spin and can be detected without the AHG phase, so they’re not the focus of AHG testing. Also, AHG is capable of detecting antibodies bound to red cells in vivo (direct Coombs test) as well as antibodies present in serum that can react with red cell antigens in vitro (indirect Coombs test).