In a case of cold autoimmune hemolytic anemia, the patient's serum would most likely react 4+ at immediate spin with which of the following?

In cold autoimmune hemolytic anemia, the patient's serum typically contains autoantibodies that react primarily with red blood cells at cooler temperatures, specifically at or near room temperature. This condition tends to be mediated by IgM antibodies, which are known to react with the I antigen present on group O and other blood group cells.

When testing against a blood group panel, which typically includes a variety of red blood cell types, the patient’s serum would show strong reactivity (4+) with all cells from a group O cell panel, as these cells express the I antigen effectively. Moreover, the patient's own cells might also react due to the presence of the same antigens, although under certain conditions, the autocontrol may sometimes appear negative depending on the extent of the patient's hemolytic activity and the specifics of the autoantibodies present.

Thus, the presence of antibodies reacting against I antigen in group O cells makes this choice the most accurate among the options provided. The focus is on the typical behavior of autoantibodies in cold autoimmune hemolytic anemia, which leads to significant reactivity across a wide variety of cells in the panel, especially group O cells.