What is the most likely explanation when all positive cold agglutinin tubes remain positive after 37°C incubation?

When all positive cold agglutinin tubes remain positive after incubation at 37°C, it suggests that there may be the presence of an antibody that is not cold agglutinins. Cold agglutinins are antibodies that typically cause agglutination at cooler temperatures (around 4°C) and typically do not react at higher temperatures, such as 37°C. The persistence of agglutination at this elevated temperature indicates that the antibodies responsible for the reaction are likely reacting under conditions that would not typically favor cold agglutinins.

This scenario can occur with other types of antibodies that might recognize the same or different antigens present on red blood cells, resulting in agglutination regardless of temperature. For instance, warm agglutinins or antibodies related to other immunological reactions may keep the agglutination response active even after the temperature is raised.

In contrast, options such as high titer cold agglutinins, contamination of the test system, or a faulty water bath would not account for the observed behavior of the agglutination remaining positive once the temperature is increased to 37°C. High titer cold agglutinins would typically only react at lower temperatures, while contamination might lead to unexpected