Detection of red cell sensitisation by antibody and complement: Current practice and future perspectives

Clinical application of a flow cytometric direct antiglobulin test

BACKGROUND

The clinical application of flow cytometric direct antiglobulin test (FC-DAT) has rarely been evaluated for patients with various diseases including immune and nonimmune hemolytic anemia.

STUDY DESIGN AND METHODS

Blood samples from 380 patients with a variety of diseases were studied using the tube direct DAT and FC-DAT. The results of tube DAT and FC-DAT were compared. The predictive values of DAT for hemolysis were evaluated.

RESULTS

Of 57 patients with autoimmune hemolytic anemia (AIHA), 6 of the 17 with a negative tube DAT (immunoglobulin G [IgG]) had a positive FC-DAT (IgG) and 23 of the 36 patients with a negative tube DAT (complement 3d [C3d]) had a positive FC-DAT (C3d). In 57 patients with AIHA, the incidence of positive results of FC-DAT (IgG) and tube DAT (IgG) were similar (42 positive vs. 40 positive); but in 323 patients without AIHA, the incidence of positive FC-DATs (IgG) was higher than that of tube DAT (IgG; 47 positive vs. 9 positive). The higher incidence of positive FC-DAT (C3d) than that of tube DAT (C3d) was seen in patients with AIHA (42 positive vs. 21 positive) as well as in patients without AIHA (61 positive vs. 5 positive). Both DAT (IgG) and DAT (C3d) positive has highest positive predictive value for hemolysis, followed by DAT (IgG) alone positive and DAT (C3d) alone positive.

CONCLUSIONS

FC-DAT is a complementary test for diagnosing AIHA. There is a synergistic effect of the red blood cell-bound IgG and complement in predicting hemolysis.

An enzyme-linked immunosorbent assay for complement regulatory proteins and membrane-bound immunoglobulins on intact red blood cells

We have developed an ELISA technique to examine RBC-bound molecules in autoimmune disorders. In particular, the technique has enabled us to investigate the role of some complement regulatory proteins in immune complex transport and to suggest that decay accelerating factor (DAF) may be involved in this process. In both autoimmune haemolytic anaemia (AHA) and systemic lupus erythematosus (SLE) a sub-set of individuals was identified, on the basis of patterns of complement receptor 1 (CR1) expression on RBC. In these patients, CR1 identified using the monoclonal antibody E11 was low or absent whereas CR1 identified using a DAKO monoclonal antibody (C3RTo5) was present at normal levels.