What could lead to a false negative result in an indirect antiglobulin test (IAT)?

A false negative result in an indirect antiglobulin test (IAT) can occur when the concentration of red blood cells (RBCs) in the test is too high. This is often referred to as using a too heavy cell suspension. When there are excessive amounts of cells, the antibodies present in the serum may not have sufficient access to bind to the antigens on the RBCs. As a result, this can prevent the visualization of any potential agglutination that would indicate a positive reaction.

In contrast, over-reading could lead to a false positive, as it involves misinterpreting the results of the test rather than failing to detect antibodies. IgG-coated screening cells should enhance the sensitivity of the IAT and typically do not contribute to false negatives. Finally, adding an extra drop of serum might lead to a stronger reaction rather than obscuring it. Hence, it is crucial to ensure the correct concentration of cell suspension is used to avoid the risk of a false negative outcome.