Collaborative studies to establish WHO International Reference Reagents for diphtheria and tetanus antitoxin for use in the flocculation test.

Here we report the results of the collaborative studies to establish a WHO International Reference Reagent (IRR) for Diphtheria Antitoxin for use in Flocculation Test (coded 23/102) and a WHO IRR for Tetanus Antitoxin for use in Flocculation Test (coded 21/230). The candidate IRRs were evaluated using the Ramon flocculation test method against the WHO International Standard (IS) for Diphtheria Toxoid for use in Flocculation Test and the IS for Tetanus Toxoid for use in Flocculation Test, accordingly. The results demonstrated that the IRRs are fit for purpose for use in the flocculation test, and the results of an accelerated thermal degradation study indicated that the materials will have good long-term stability. There are no units assigned to these reference reagents since they must be pre-calibrated against the respective toxoid IS in each laboratory before use.