IgG is not the only inhibitor of IgE in the RAST test.

Blocking phenomenon of the RAST test was studied in the sera of 50 different patients. Specific levels of IgE and IgG against 11 common foods were evaluated by ELISA. Results showed that decreases in IgG levels by protein-A were not always followed by IgE increases. In this regard, we found three different combinations in the levels of IgE and IgG: (1) an IgG decrease followed by IgE increase (29%); (2) an IgG increase followed by IgE decrease (18%); and (3) both IgG and IgE decrease (28%). From these results we concluded that IgG is not the only inhibitor of the RAST test.