In interpreting cold agglutinin titer results, what is indicated by a titer of 1:128 at 4°C?

A titer of 1:128 at 4°C indicates a significant presence of cold agglutinins, showing that the patient's serum has the ability to agglutinate red blood cells at this temperature. Cold agglutinins are typically antibodies, often of the IgM class, that can cause agglutination of red blood cells in cold temperatures.

A titer of 1:128 suggests that at a dilution of 1 part serum to 128 parts saline, agglutination is still occurring, which is a clear indicator of a positive result in the context of cold agglutinin testing. This finding is significant as it suggests an underlying condition, such as an autoimmune disorder or an infection, that may be associated with the production of these antibodies. Therefore, the titer of 1:128 is interpreted as positive, confirming the presence of cold agglutinins in the patient’s serum.

Lower titers, such as 1:64, would indicate a weaker reaction, while a titer of 1:256 would suggest a stronger reaction, which would not align with the result observed. A negative reaction would mean no detectable agglutination, which is also inconsistent with the observed titer