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Why are direct elisas sometimes referred to as sandwich elisas?
Wiki User
∙ 13y ago
Direct ELISAs are sometimes refered to as sandwich ELISAs because unlike the indirect ELISA in which the antigen is binded nonspecifically to the ELISA plate, an antibody is first plated that will capture the antigen. Next, an enzyme-linked antibody is plated and lastly a substrate which creates a measurable color change (OD). The two antibodies "sandwich" the antigen.
Wiki User
∙ 13y ago
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What do you do if you are afraid that you might be HIV positive since your boyfriend had an STI but the time he got tested for HIV he was negative and that was in August last year?
* Simple/Rapid Tests * Enzyme Linked Immuno Sorbent Assays (ELISAs) * Confirmatory Assays (such as Western Blot, line immuno assays) * CD4 technologies * HIV Viral Load The new rapid tests are combined antigen-antibody tests. Is such a test is negative the chances are that the person is negative. But remember the test tells you the status when the test was taken and nothing about what has happened afterwards. STI in itself does not say anything about HIV infection, but have you got STI you may also have got HIV at the same time or under similar conditions. At least your behaviour might be exposing you to the risk
What is interassay coefficient of variation?
The formula for coefficient of variation is %CV = standard deviation/mean X 100 (CV's are reported in percentage form). So say you're testing for fibrinogen in blood, and you run your standards or your controls three times. The INTRAassay CV is the CV for the three sets of standards in that one assay. You would calcuate the mean and standard deviation for Standard 1, Standard 2, etc. and come up with the CV for each and then average the CVs of each standard to come up with the intraassay CV. This shows the amount of variation among the standards for that one test. Now say you run a set of blood samples on Monday and then run another set on Tuesday with a second set of plates or wells. The INTERassay CV is the amount of variation between the standards you used on Monday and the standards you used on Tuesday. You would calculate the mean and standard deviation for Standard 1 (Day 1 and Day 2), Standard 2 (Day 1 and Day 2), etc. to come up with the CV for each and then average the CVs like before. This gives you the interassay CV. A lot of ELISAs will actually calculate the CV of each standard for you.
How do lab tools improve the observations made by a scientist?
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Can you have an accurate HIV test after 8 days?
AnswerHIV Duo Testing (ELISA IV), which detects the HIV-1-P24 antigen -- a definitive precursor of HIV -- has a superb success rate at as little as 7 days. However, a 28-day test is recommended, and apparently produces a higher degree of accuracy. AnswerHIV Duo detects both antibodies to HIV as well as p24, which is part of the virus itself. Antibodies are only formed after exposure to the antigen, so the antigen is detectable earlier than antibodies. This test reduces the window period significantly, and as the previous answer said, has a good sensitivity at even 7 days.However, we must remember that each individual is different, and may "incubate" the virus for a different time to other people. In any particular individual, 4th generation ELISAs such as the Duo will only pick up antigen 7-10 days before the antibody appears. So those who would become positive on an antibody-only assay at 8 weeks will become positive on the Duo at 6.5-7 weeks. HIV first has to replicate locally before it spreads to the lymph nodes, and only after that does the major viraemia appear, and it is that viraemia that is detected by the p24 part of the assay. If the local replication occurs quickly, the person will be positive sooner.There will always be the very small percentage who take longer.There is one pont which is not logical.So those who would become positive on an antibody-only assay at 8 weeks will become positive on the Duo at 6.5-7 weeks.The antibody production is the host response to the antigen there may be differences in the time period of host response so it would be wrong to conclude the presence of antigen relative to antibody production.assume A and B are infected (read antigen present at point t(time)) A takes x period to seroconvert(antibody production) and B takes Y period to seroconvert.but both had antigen at t(time) hence it would be wrong to assume presence of antigen in A as x-c and B as Y-c (c is a constant). both would be different.Visit: drtanandpartners.com
