Accurate measurement of low IgE concentrations is technically difficult. In this paper results obtained by a direct sandwich and three inhibition methods of radioimmunoassays are compared. For values above 50 U/ml good correlation was obtained with all methods. Below 50 U/ml, however, the inhibition methods tended to yield falsely high values. For very low concentrations, 1–10 U/ml the best correlation was obtained between the direct sandwich test (PRIST*) and the inhibition test using a correction factor to allow for the non-specific effect of serum.
The four methods were used to quantify IgE in cord serum samples from healthy individuals. The mean value obtained by PRIST was 0.4 U/ml and by the inhibition test, using a correction factor, 0.6 U/ml respectively. Because of its greater simplicity the direct sandwich test is recommended.