In a transfusion scenario, pretransfusion antibody screening showed no agglutination until IgG sensitized cells added; repeat testing detected an antibody at the antiglobulin phase. What explains the original result?

In a transfusion scenario, pretransfusion antibody screening showed no agglutination until IgG sensitized cells added; repeat testing detected an antibody at the antiglobulin phase. What explains the original result?

• A. Red cells were overwashed
• B. Centrifugation was prolonged
• C. Patient's serum was omitted from the original testing
• D. Antiglobulin reagent was neutralized

Answer: (C)

In antibody screening, antibodies present in the patient’s serum must bind to corresponding antigens on screening red cells, and the antiglobulin reagent (AHG) then detects those bound IgG by causing agglutination. If the patient’s serum was not added in the original test, there would be nothing for the screening cells’ antigens to bind to, so no agglutination would occur during the incubation or at the AHG phase. When the test was repeated correctly with the patient’s serum included, an antibody was detected at the antiglobulin phase, which fits the expected pattern for IgG antibodies detected by indirect antiglobulin testing. Thus, omitting the patient’s serum explains the initial negative result.

In antibody screening, antibodies present in the patient’s serum must bind to corresponding antigens on screening red cells, and the antiglobulin reagent (AHG) then detects those bound IgG by causing agglutination. If the patient’s serum was not added in the original test, there would be nothing for the screening cells’ antigens to bind to, so no agglutination would occur during the incubation or at the AHG phase. When the test was repeated correctly with the patient’s serum included, an antibody was detected at the antiglobulin phase, which fits the expected pattern for IgG antibodies detected by indirect antiglobulin testing. Thus, omitting the patient’s serum explains the initial negative result.