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November 1988

Invalid Equation for Conversion of Indirect Hemagglutination Titers to International Units-Reply

Am J Dis Child. 1988;142(11):1140. doi:10.1001/archpedi.1988.02150110018007

In Reply.—We wish to respond to the letter from Drs Wilkins and Wehrle concerning our previous publication. We agree that toxin neutralization (TN) tests are superior, in principle, to IHA tests for determining neutralizing antibody titers, because the latter may be responsive to antibodies that bind toxin without neutralizing it. For this reason, we used a tissue culture TN test to assay antibody titers against diphtheria toxin. However, no such assay was available for antibodies against tetanus toxin and, given the large number of sera to be evaluated, we preferred IHA to the alternative, the cumbersome mouse protection test. Contrary to the opinions cited by Drs Wilkins and Wehrle, we note that many researchers have found good correlation between the IHA and mouse tests for tetanus antitoxin titers,1-6 including Dr Nyerges. Drs Wilkins and Wehrle cited two 1962 articles by Dr Nyerges (with Dr Surján) reporting a poor correlation between