The Po River Delta epidemiological survey: Reference values of total serum IgE levels in a normal population sample of North Italy (8–78 yrs)

The aim of this paper was to define, for the first time in Italy, normal levels of total serum IgE in a general population sample of North Italy. Total serum IgE in 1905 subjects, living in Po Delta area (near Venice), were measured by PRIST method. Normal values were derived from 558 subjects without asthma and/or asthmatic/rhinitic symptoms, noncurrent smokers, skin prick-test negatives (‘normals’). Cut-off values to differentiate ‘normals’ from the remaining part of the sample (‘others’), from asthmatic, and from rhinitic subjects, were established with the IgE value midway between the upper limit of the 95% confidence intervals (CI) of the geometric mean for ‘normals’ and the lower limit for ‘others’, asthmatics, and rhinitics, respectively. Geometric mean of normal children–adolescents was 45 kU/L (SD: 2.6; 95% CI: 38–63). In normal adults geometric mean was 29 kU/L (SD: 3.3; 95% CI: 25–40) in males and 19 kU/L (SD: 3.8; 95% CI: 16–22) in females. The diagnostic sensitivity of IgE test was low, while the specificity was very high. A good positive predictive value in discriminating ‘normals’ from ‘others’ was found, on the contrary, we found a good negative predictive value in discriminating ‘normals’ from asthmatics or from rhinitics. In conclusion, our results confirm that it is necessary to provide separate total serum IgE reference values for what concerns age in children–adolescents and in adults, and gender, in adults. Low level of total serum IgE are helpful to exclude allergic asthma or rhinitis.