Isotopic and Enzymatic IgE Assays in Non‐Allergic Subjects

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Abstract
In order to establish normal values in an adult population for serum IgE concentration, sera were obtained from 446 ambulatory Canadian Caucasian subjects with negative allergy histories. A standard isotopic procedure, the Phadebas paper radioimmunosorbent test (PRIST), was compared with the new enzymatic counterpart, the Phadezyme PRIST. By the isotopic method, serum IgE concentrations in women and men were comparable from one age group to another with no age‐related trend in the seven age groups examined (15–20, 21–30, 31–40, 41–50, 51–60, 61–70, above 70). The median and 95th percentile units (U)/ml respectively were 17.5 and 145 for 224 women and 25.5 and 275 for 222 men. Mean values ± 1 SD for women were 43 ± 102 and for men, 58 ± 137. Levels were significantly higher in men as a group. Sera with IgE concentrations above 100 U and a sampling of additional sera were tested for specific IgE antibodies to 13 common allergens by the radioallergosorbent test (RAST). After exclusion of RAST‐positive sera, the mean U/ml values ± 1 SD were 22 ± 29 for 204 women and 37 ± 54 for 196 men. Geometric mean U/ml values for these sera were 14.6 for women and 22.3 for men and the median and 95th percentile U/ml respectively for the women were 15 and 66, for the men, 24 and 135. These 95th percentile values are considered the upper limits of normal in this population. The RAST identification of antibodies to allergens to which sensitization was demonstrated provided a potential explanation for serum IgE concentrations above 100 U/ml in less than 30% of the sera in this population with negative allergy histories. The isotopic method and the counterpart enzymatic method (Phadezyme PRIST) were highly comparable; the correlation coefficient (r) for all the sera was + 0.93 (P < 0.001). IgE levels were significantly higher in male smokers than non‐smokers by both methods but these differences were not significant in women.