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

BACKGROUND

Determination of specific IgG antibodies is important for the diagnosis of extrinsic allergic alveolitis (EAA). Various evaluations have however 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 control system and to analyse, what the explanations for the different outcomes from various laboratories might be.

METHODS

In the past 4 years 5 sera from patients suffering from EAA or healthy 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 sent back to the reference center for statistical evaluation. Precipitating techniques were used in 8 laboratories during the first mailings, but were gradually exchanged by automated ELISA systems being employed in 8 laboratories in the last mailing.

RESULTS

1127 values were determined in 105 expectedly positive sera and 1003 in 94 negative samples. Of the 562 values obtained with precipitation techniques 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 and even 95.5% for the UniCAP System. Regarding the specificity however, 93.0% of the expected negative results were correct negative using precipitation methods, whereas merely 75.2% were negative with the EnzyDex System and only 22.5% using the UniCAP System. Moreover 35.8% of the results using this latter method were false-positive.

CONCLUSIONS

The traditional precipitation techniques proved not only technically difficult to perform, but also unreliable, difficult to reproduce, insensitive 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 technique concerning handling, automation, and quality criteria like sensitivity quite well, but not for specificity. Both techniques urgently need external standardization in order to make the results comparable among the different systems and methods; the danger of potentially false-positive results, pretending sensitizations that might be clinically irrelevant in several cases, is high.