Relationship between antigen-specific IgE antibody (RAST) and total serum IgE levels.

Although the total serum IgE level is generally higher in atopic than in non-atopic individuals, high total serum IgE levels and atopic diseases are not invariably associated. In 42 atopic patients with the total serum IgE levels less than 100 U/ml, 27% of RAST against 14 allergens were positive whereas in 45 atopic patients with the total serum IgE levels greater than 500 U/ml, 57% of RAST against 14 allergens were positive. The mean RAST values against four grass antigens expressed as a percentage of antigen-disc bound radioactivities were significantly lower in the group with the lower total serum IgE levels. Low or normal total serum IgE levels are likely to be found in atopic patients who are allergic to a relatively few grass antigens.