Passive haemagglutination inhibition for quantitation of red cell associated IgG.

Passive haemagglutination inhibition (PHI) was adapted to quantitate red cell associated IgG. Twenty one patients with autoimmune haemolytic anaemia (AIHA) had a raised red cell associated IgG, mean (SD) = 5.783 (6.183) ng/10(6) red blood cell compared with that of 69 subjects with a red cell associated IgG of 0.433 (0.349) ng/10(6) red blood cell. Thirteen of 14 blood donors with a positive direct antiglobulin test (DAGT) had a normal red cell associated IgG. The only blood donor with positive DAGT and raised red cell associated IgG had AIHA. Studies of red cell associated IgG in other groups of patients were also undertaken. The technique is simple, does not require the use of sophisticated equipment, and is suitable as a routine test in hospital laboratories. The results of red cell associated IgG by PHI are reproducible and clinically relevant.