# Council Directive 98/57/EC of 20 July 1998 on the control of Ralstonia solanacearum (Smith) Yabuuchi et al., Division: Interpretation of ELISA test results:

Extent: E+W+S+N.I.

The ELISA test is negative if the average optical density (OD) reading from duplicate sample wells is < 2x OD of that in the negative sample extract control well, providing the OD for the positive controls are all above 1,0 (after 90 minutes incubation with the substrate) and are greater than twice the OD obtained for negative sample extracts.
The ELISA test is positive if the average OD readings from duplicate sample wells is > 2x OD in the negative sample extract well provided that OD readings in all negative control wells are < 2x those in the positive control wells.
Negative ELISA readings in positive control wells indicate that the test has not been performed correctly or that it has been inhibited. Positive ELISA readings in negative control wells indicate that cross-contamination or non-specific antibody binding has occurred.

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Source: https://www.legislation.gov.uk/eudr/1998/57/annex/II/section/VI/division/A/division/8/division/3 (the official version)
Page: https://openlegislation.uk/eu-directive-1998-57/annex-II/section-VI/division-A/division-8/division-3
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.