IgG antibodies typical for extrinsic allergic alveolitis - An inter-laboratory quality assessment

Background: Determination of specific IgG antibodies is important for the d iagnosis of extrinsic;allergic alveolitis (EAA). Various evaluations have h owever shown, that current methodology lacks sufficient standardization in that the employment of different sources of extracts and techniques makes a comparison of data from one laboratory to another almost impossible. Objective: The aim of this study is to establish an external quality contro l system and to analyse, what the explanations for the different outcomes f rom various laboratories might be. Methods: In the past 4 years 5 sera from patients suffering from EAA or hea lthy controls were sent every 6 months to 11 different allergy laboratories in Austria. The determination of specific IgG antibodies against antigens that are typical for this disease were requested. Results were gained with the method routinely used in the respective laboratory, and then Sen. back to the reference center for statistical evaluation. Precipitating technique s were used in 8 laboratories during the first mailings, but were gradually exchanged by automated ELISA systems being employed in 8 laboratories in t he last mailing. Results: 1127 values were determined in 105 expectedly positive sera and 10 03 in 94 negative samples. df the 562 values obtained with precipitation te chniques in positive sera, only 52.0% were reported to be positive, and the results varied considerably among laboratories and antigens. In contrast, 93.3% were positive with commercially available ELISA techniques, with 92.3 % for the EnzyDex System (R) and even 95.5% for the UniCAP System (R). Rega rding the specificity however, 93.0% of the expected negative results were correct negative using precipitation methods, whereas merely 75.2% were neg ative with the EnzyDex System (R) and only 22.5% using the UniCAP System (R ). Moreover 35.8% of the results using this latter method were false-positi ve. Conclusions: The traditional precipitation techniques proved not only techn ically difficult to perform, but also unreliable, difficult to reproduce, i nsensitive and impractical in daily laboratory work. They suffer from that many draw backs, that their use in daily routine cannot be recommended any more. Automated ELISA systems seem to fulfill the criteria for a routine te chnique concerning handling, automation, and quality criteria like sensitiv ity quite well, but not for specificity. Both techniques urgently need exte rnal standardization in order to make the results comparable among the diff erent systems and methods; the danger of potentially false-positive results , pretending sensitizations that might be clinically irrelevant in several cases, is high.