The European Consensus Finding Study Group on Autoantibodies is currently formed by 43 European laboratories involved in the field of serological diagnostics in rheumatic diseases. The aim of this group is to work towards achieving common consensus in this field: a laboratory result should be the same, wherever the result is obtained.

The Steering Committee of the Consensus Finding Study Group tested 24 candidate sera that had been contributed by the participating laboratories. Ten sera were selected for the annual serum round. This year, special emphasis was put on anti-DNA antibody testing. For this purpose four sera were included that contained different specificities of anti-DNA (Table 1). The remaining six sera were positive for a variety of autoantibodies (Table 1).

For the first time, a dedicated computer program was used to allow more easy data entry and statistical analysis. Next to the 10 sera, a CD-ROM containing 20 HEp-2 cell staining patterns was dispatched to the participating laboratories. The CD-ROM also contained the spreadsheets to be filled in by the participants.

Results were returned by 38 out of 43 participating laboratories. The data were discussed at a satellite meeting during the 24th European Workshop on Rheumatology Research in Berlin and were published on the website of the Sanquin Blood Supply Foundation in Amsterdam (via a link distributed to the participants). In depth analysis of individual results compared with the consensus were sent to the participants.

In general, the participants reached a high degree of consensus for most of the samples. The results for anti-DNA were very promising. A perfect consensus was reached for the absence of dsDNA antibodies in an anti-ssDNA specific serum (serum 8). The absence of false positive results showed that assays measuring anti-dsDNA antibodies have been improved such as to exclude detection of anti-ssDNA. Serum 9 was obtained from a rheumatoid arthritis patient who had been treated with anti-tumour necrosis factor alpha (Infliximab) and developed anti-dsDNA antibodies, yet showed no clinical signs of systemic lupus erythematosus. Using different assays, divergent results were obtained. Most laboratories found anti-dsDNA antibodies by the indirect immunofluorescence technique (substrate Crithidia luciliae), whereas anti-dsDNA ELISAs were negative. For this sample most (commercial) Farr assays showed positive reactions. Detailed analysis of the serum in Amsterdam showed the presence of low avidity IgM and IgG antibodies to dsDNA. In order to understand the cause of the discrepancies the influence of choice of assay will be studied in more detail. Divergent results, depending on the method for detection, were also found for antibodies to SS-A. Obviously, ELISA-based techniques were more sensitive. Unfortunately, most ELISAs do not distinguish between anti-SS-A 52 and anti-SS-A 60 antibodies. The clinical relevance of the lower limit of detection has to be established in the future. We will include a more detailed method analysis in the next rounds.

There was general agreement among the participating laboratories that these Consensus Rounds should be continued, including the HEp-2 cell pattern recognition CD-ROM effort. It was decided to focus next round on anti-phospholipid antibodies. For information about the study group please contact Ruud Smeenk r.smeenk@sanquin.nl.