European Sero-Epidemiology Network: standardisation of the results of diphtheria antitoxin assays

A European Sero-Epidemiological Network (ESEN) was established with the aim to co-ordinate and harmonise serological surveillance of immunity to commu nicable diseases in Europe. In this study the inter-laboratory standardisat ion of diphtheria toxin antibody measurements is reported. A standard panel of 162 sera was tested by the participating laboratories using an in vitro assay of their choice: VERO cell toxin neutralisation assay (NT), double-a ntigen delayed time-resolved fluorescence immune-assay (DA-DELFIA), double- antigen enzyme-linked immunosorbent assay (DAE), toxin binding inhibition t est (ToBI) and an indirect enzyme-linked immunosorbent assay (ELISA). The r esults were standardised using regression against the NT. The variations du e to inter-laboratory and inter-assay variation,which would otherwise make it difficult directly to compare the main serum bank results by the differe nt laboratories and the various assays were successfully minimised by the s tandardisation. The regression equations obtained will be used to transform the respective local results of testing the main serum bank into the refer ence test unitages. This study also gave the opportunity to compare the var ious assays within and between laboratories. This demonstrated a very high correlation between DA-DELFIA, DAE, ToBI and the NT. The ELISA showed a goo d correlation, too, however sera below some 0.1 IU/ml were overestimated. ( C) 2000 Elsevier Science Ltd. All rights reserved.