Quantitation of red cell-bound IgG by an enzyme-linked antiglobulin test in the patients with warm-type autoimmune haemolytic anaemia.

We have previously reported the evaluation of a gel-direct antiglobulin test and enzyme-linked antiglobulin test (ELAT) in the laboratory diagnosis of autoimmune haemolytic anaemia (AIHA). We now report our experience with quantitative ELAT performed on a large group of patients under long-term observation. The number of IgG molecules/red blood cell was determined in 658 blood samples from 268 randomly selected patients with warm-type AIHA. Eighty-six patients were tested every 2-4 weeks for several months. Laboratory signs of haemolysis were present in 65.7% of blood samples with a small amount of red cell-bound autoantibody (< 200 IgG molecules/red blood cell) and in 70.4% of blood samples with moderately coated red blood cells (200-1000 molecules/red blood cell). Haemolysis was demonstrated in 87.9% samples with > 1000 IgG molecules/red blood cell, which were predominantly IgG3 and C3 complement, the qualitative factors that may increase haemolysis. In 79% of periodically tested patients, the number of IgG autoantibody molecules/red blood cell decreased and this correlated with the improvement of haemolysis parameters. The number of IgG molecules varied in 21% of AIHAs and was associated with poor prognosis.