|home access test
Jul 11, 2001
hi dr, i recently found out that home access uses 1st generation Elisa tests (and IFA for confirmation) and decided to inquire for myself to be sure. below is the response i received. would you agree or disagree with the explanation? they claim that by three months there is no difference between a 1st or 3rd gen. test in accuracy. i would like to know your opinion on this matter. thanks.
"We do use the first generation ELISA, which uses viral lyzates as antigen. The difference with the third generation ELISA is that the latter uses recombinant proteins as antigens. Because of the fact that recombinant proteins are purer than viral lyzates, it's possible to amplify the reaction with antibodies to HIV-1 more.
Two considerations. Firstly, by three months, there is no difference between 1st and 3rd generation EIA. Secondly, even the early difference between 1st and third generation is eliminated because of confirmatory testing. We can safely tell that accuracy in 3 months is close to 100 or at least more than 99.
To the first point. The third generation EIAs detect antibodies 5-10 days earlier than the first generation during seroconversion, the period when the HIV-1 infected person is turning from antibody-negative to antibody-positive. It means that after HIV-1 exposure, on average, in a week half of individuals become reactive with EIA, if tested with 3rd generation EIA. 1st generation will pick up these infected individuals in two weeks. As practically all individuals turn reactive after two moths, in three months, there is no difference between different EIA generations.
To the second point. The EIA reactive samples should be confirmed by Western Blot or IFA (as in our system). Western Blot and IFA turned indeterminate at the time when 1st generation EIA becomes reactive, in around 14 days. Western Blot and IFA become positive after 40-50 days, on average. Hence, the infected individuals tested reactive with the third generation BEFORE 1st generation can pick them up, will test negative with confirmatory test. Algorithms using third and first generation EIA, but the same confirmatory testing, will return THE SAME results.
The difference in the third and the first generation matters ONLY during blood testing of donors as blood is rejected if only EIA is reactive.
We prefer the first generation ELISA because it is less specific and can pick most of HIV-2 infected persons and abnormal HIV-1 samples."
| Response from Dr. Holodniy
Not a bad explanation.
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