Which antibody gives a refractile mixed-field appearance?

The antibody responsible for the refractile mixed-field appearance is Anti-Sda. When Anti-Sda is present in a blood sample, it reacts with certain antigens found on red blood cells in a manner that can lead to a characteristic mixed-field agglutination pattern. This results in an appearance where some cells are agglutinated while others remain unagglutinated, leading to the striking mixed-field effect that can be observed under the microscope.

This mixed-field reaction occurs because Anti-Sda may bind to red blood cells expressing the Sda antigen, resulting in a mixture of agglutinated cells and free cells that do not react, thus creating a refractile or varying appearance within the field of view. Such reactions are particularly noticeable when testing with group O cells, which can express the Sda antigen variably, contributing to the mixed-field effect.

In contrast, antibodies like Anti-K, Anti-Dia, and Anti-s do not produce the same mixed-field appearance as Anti-Sda. They typically lead to more consistent agglutination patterns without the distinct refractile quality associated with mixed-field reactions.