A false negative indirect antiglobulin test can result from which of the following?

• A. Inadequate washing of red blood cells
• B. Very short incubation
• C. Using LISS
• D. Excessively high cell concentration

Answer: (A)

In the indirect antiglobulin test, you rely on antibodies in the patient’s serum to bind to antigens on the reagent red cells during incubation, and then you detect those bindings with anti-human globulin (AHG). Thoroughly washing the red cells after incubation is essential to remove all unbound antibodies. If washing is inadequate, residual free antibodies and serum proteins remain in the mixture, which can interfere with the AHG step and prevent the lattice formation needed to see agglutination. This can mask a true antibody reaction, producing a false negative result.

Short incubation reduces the opportunity for antibody binding, which can also cause false negatives but is not the scenario described here. Using LISS actually enhances antibody binding and lowers the chance of a false negative, so it wouldn’t cause this outcome. Excessively high cell concentration is not a typical cause of false negatives in this test.