Clinically Significant

A term used to describe the fact that a particular blood group antibody can cause one of two problems:

1. Hemolytic transfusion reactions
2. Hemolytic disease of the fetus/newborn (HDFN)

Most significant antibodies are IgG antibodies rather than IgM. IgG antibodies typically react at or near body temperature (37 C) and are more likely to damage incompatible transfused red blood cells than antibodies that react best at lower temperatures. Further, IgG antibodies are transported across the placenta into the fetal circulation, and are more likely to cause HDFN. However, this does NOT mean that all IgM antibodies are insignificant! The antibodies in the ABO blood group system are IgM to a great extent, and they can cause serious hemolytic transfusion reactions.

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