Quantitation of IgG on Erythrocytes: Correlation of Number of IgG Molecules per Cell with the Strength of the Direct and Indirect Antiglobulin Tests

Abstract

The number of IgG molecules bound to the erythrocyte surface for a given agglutination score in the antiglobulin test was studied with several different examples of anti-D, anti-E, anti-c, anti-Kell, anti-Fya, anti-Jka and immune anti-A antisera. The serological scores show a significant correlation with the mean values for bound IgG molecules within a restricted range, although the number bound for a given score may vary by up to 20%. The limit of detection was 100-120 IgG molecules per cell and when over 1,000 were bound, the cells were completely agglutinated. Anti-Kell bound under low ionic strength saline conditions required a greater number of molecules for a given agglutination strength. The relatively low levels of bound IgG necessary to give strong agglutination make the direct antiglobulin test (DAT) less valuable for following the progress of auto-immune haemolytic anaemia (AIHA) than a quantitative test. The latter test does not, however, provide any additional information in AIHA cases with a negative DAT as in these the anaemia does not appear to be due simply to the number of bound IgG molecules. Detection of certain antibodies may not be achieved simply by increasing the sensitivity of the antiglobulin test when correctly performed.

Clinical Patterns and Hematological Spectrum in Autoimmune Hemolytic Anemia

“…[26] Various other studies give the threshold of IgG molecules to be detected by antiglobulin test to be anywhere from 100 to 500. [78] In the above context, AIHA with low titers of antibodies may present with negative DAT i.e. DAT negative AIHAs.…”

Monocyte-Erythrocyte Interaction in Autoimmune Haemolytic Anaemia in Relation to the Number of Erythrocyte-Bound IgG Molecules and Subclass Specificity of Autoantibodies

“…In 29 out of the above mentioned patients and 3 donors, the total number of erythrocyte-bound IgG molecules was evaluated by a quantitative anti-antiglobulin test with Iz5I anti-IgG [22,23]. Values were corrected for the binding to trypsin-treated cells incubated with IZ5I anti-IgG as a control.…”

Quantification of IgG on erythrocytes of patients and normals by a radio‐ligand‐binding assay

“…IgG bound to erythrocytes has been detected in blood transfusion serology by agglutination with polyclonal anti-human IgG reagents. The sensitivity of these agglutination tests has been increased by substituting tile tests with tube spin tests and by incorporating low ionic strength solutions and lower cell concentrations during sensitization (Mollison et al, 1987). Another very economic and sensitive method for the detection of bound IgG in antiglobulin tests uses capillary tubes (Chown & Lewis, 1957).…”