Immunoglobulin E assayed after pepsin digestion by an automated and highly sensitive particle counting immunoassay: application to human cord blood.

We describe in this article a fully automated, universal assay for serum IgE after pepsin digestion of the sample and subsequent assay of the released Fc" epsilon fragment by particle counting immunoassay (PACIA). The sensitivity and the range of the assay were easily modulated by changing the concentration of dextran in the reaction medium. In the application to cord serum, the sensitivity reached 0.1 IU/ml in 30 min incubation time and with a throughput of 50 analyses per hour. Within-day and between-day coefficients of variation did not exceed 7.6% for IgE levels covering a wide range of the standard curve. Dependable accuracy was demonstrated by linearity tests, analytical recoveries (89% to 112%), and correlation with PRIST on 48 samples from children ages 1 to 14 yr (y = 0.97x + 5.92; r = 0.987). Minor discrepancies between the two methods were attributed to a slight serum effect in PRIST. PACIA applied to 348 cord serum samples demonstrated a statistically significant influence of sex and race on the cord IgE level. In European neonates boys had significantly (p = 0.019) higher geometrical mean cord IgE levels (n = 142; 0.46 IU/ml; range less than 0.10 to 30 IU/ml) than girls (n = 146; 0.33 IU/ml; range less than 0.10 to 8.0 IU/ml), which was attributed to a predominance of boys (chi 2 = 4.29; p less than 0.05) having more often elevated cord IgE (less than 1.20 IU/ml) than girls. Neonates of African-Asian origin had significantly (p less than 0.00005) higher cord IgE levels (n = 60; 1.05 IU/ml; range less than 0.10 to 125.0 IU/ml) than European neonates (n = 288; 0.39 IU/ml; range less than 0.10 to 30.0 IU/ml).