Which result demonstrates an antibody that reacts only at the antiglobulin (AHG) phase in transfusion testing?

Which result demonstrates an antibody that reacts only at the antiglobulin (AHG) phase in transfusion testing?

• A. IAT positive at immediate spin
• B. IAT positive at 37C
• C. IAT negative at AHG
• D. IAT positive at AHG

Answer: (D)

Antibody detection in transfusion testing relies on distinct phases that reveal different types of antibodies. Immediate spin mainly picks up IgM antibodies that react at room temperature, while the 37°C phase detects warm-reacting IgG antibodies that react at body temperature. The antiglobulin (AHG) phase is used to reveal IgG antibodies that have already bound to red cells but will not cause visible agglutination without the antiglobulin reagent. If an antibody reacts only at the AHG phase, the test would be negative at immediate spin and negative at 37°C, then become positive when AHG is added. That pattern shows an IgG antibody that is sensitized to the red cell surface but requires the AHG reagent to bridge the Fc portions and produce agglutination. So the result described as IAT positive at AHG demonstrates an antibody that reacts only at the AHG phase. The other patterns—positive at immediate spin or 37°C, or negative at AHG—do not reflect AHG-only reactivity.

Antibody detection in transfusion testing relies on distinct phases that reveal different types of antibodies. Immediate spin mainly picks up IgM antibodies that react at room temperature, while the 37°C phase detects warm-reacting IgG antibodies that react at body temperature. The antiglobulin (AHG) phase is used to reveal IgG antibodies that have already bound to red cells but will not cause visible agglutination without the antiglobulin reagent.

If an antibody reacts only at the AHG phase, the test would be negative at immediate spin and negative at 37°C, then become positive when AHG is added. That pattern shows an IgG antibody that is sensitized to the red cell surface but requires the AHG reagent to bridge the Fc portions and produce agglutination. So the result described as IAT positive at AHG demonstrates an antibody that reacts only at the AHG phase. The other patterns—positive at immediate spin or 37°C, or negative at AHG—do not reflect AHG-only reactivity.