Total serum IgE: adult reference values in Valencia (1981-2004). Usefulness in the diagnosis of allergic asthma and rhinitis.

Background: The reference values for total serum IgE are accepted to vary according to the geographical area involved. In 1981 we published the reference values for a donor population in the city of Valencia (Spain) and its metropolitan area. Since then, we have noted an increase in the prevalence of asthma and rhinitis in countries with a Western lifestyle, including Spain.
Aim: To update the adult reference values for total serum IgE in the city of Valencia and its metropolitan area, and to determine their diagnostic usefulness in asthma and allergic rhinitis.
Material and Methods: We studied two groups of 69 and 100 individuals each. One group comprised apparently healthy blood donors, as assessed by a routine blood bank study protocol and the application of a questionnaire to exclude perceived allergic or parasitic diseases, while the other group consisted of individuals with atopic respiratory disease (bronchial asthma and allergic rhinitis) studied in our service in the same time period (spring 2004). Total serum IgE was determined by the UniCAP method developed by Pharmacia.
Results: The geometric mean of total serum IgE among blood donors was 46.65 kU/l (95% CI: 15.5-77.8) versus 204.29 kU/l (95% CI: 93.3-515) among allergic subjects. The difference between the two groups was statistically significant. No significant difference was found between our donor sample in 1981 and the sample in the present study. Establishing an arbitrary cut-off point of 1.65 standard deviations (SD)(equivalent to 95 % of the donor population), we obtained a figure of > 183 kU/l whereby 44% of all allergic individuals presented a value below this cut-off point. To practical effects, these allergic patients behaved as low responders (LRs) in relation to total IgE, whereas the remaining individuals were high responders (HRs) in relation to total IgE.
Conclusions: Our data confirm the current validity of the reference values obtained in 1981, which continue to be significantly different from those of the UniCAP method for Swedish donors. The population of allergic subjects can be divided into two subgroups: subjects with total IgE levels similar to those of the donors, which we refer to as LRs, and which represent 44% of all allergic subjects, and a second subgroup with total IgE values above those of the donors (HRs), who would therefore be the only subjects that would be identified by individual serum IgE study.