Reduced isohemagglutinin level 2018-11-22T15:04:35Z The determination of isohemagglutinins can be used to evaluate an individual's ability to mount an immune response except in persons with blood group AB. Partial absence of isohemagglutinins Level of isohemagglutinin reduced below expected concentration. An isohemagglutinin refers to the naturally occurring antibodies in the ABO blood group system (i.e., anti-A in a group B person, anti-B in a group A person, and anti-A, anti-B, and anti-A,B in a group O person). Decreased natural antibody to blood group agents Abnormal isohemagglutinin level