Comparison of procedures for measurement of IgE protein in serum and secretions.

Because of conflicting reports in the literature concerning the value of various procedures for measurement of IgE in serum and secretions, we compared four different methods, the radioimmunosorbent test (RIST), the double-antibody radioimmunoassay (RIA), the paper disc immunosorbent test (PRIST), and radial immunodiffusion (RID). The standards used in the assays were tested initially in the double-antibody RIA with the use of the reference from the World Health Organization. The results showed that RID as expected was relatively insensitive and IgE was reliably measured only above approximately 1,000 international units (IU). Moreover, certain sera containing low levels of IgE by the other procedures gave distinct precipitin zones and presumably falsely high levels of IgE protein. Thus RID may yield apparently erroneous results when used as a screening procedure for measurement of IgE levels. Among the other procedures PRIST and the double-antibody RIA showed the best agreement. With serum samples RIST yielded values for IgE in the low level range higher than those given by the PRIST and double-antibody RIA. With breast milk and colostrum, values of IgE between 120 and 690 ng/ml were found by RIST, whereas IgE was not detected by double-antibody RIA and PRIST. No evidence of an inhibitor of IgE was found in breast milk, so that the apparent elevation of IgE in breast milk by the RIST is likely false. These findings confirm prior reports of spurious elevations of IgE with the RIST and indicate the usefulness of the PRIST and double-antibody RIA for the measurement of IgE in sera and secretions.