Local lymph node assay: how testing laboratories apply OECD TG 429 for REACH purposes

The Local Lymph Node Assay (LLNA) is the official method for assessing the allergic contact dermatitis potential of chemicals for the purposes of REACH regulation. The LLNA went through a validation process that allowed the delineation of a robust protocol for performing new tests. The OECD accepted this method in 2002 and published OECD TG 429. The European Chemical Agency (ECHA) recently published data that were submitted in the registration dossiers of chemicals. This database was analysed to determine how testing laboratories apply OECD TG 429. This analysis comes after a detailed analysis of four full study reports that were also prepared for REACH purposes. Although the majority of the tests are fully compliant with OECD TG 429, some showed major deviations, and a number of others used more animals than necessary. This suggests that in vivo tests need to be planned more carefully and consciously to obtain meaningful results with the minimum animal number necessary.