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testing at 28 days - PCR or P24 antigen

There are many tests on the market and each test has its own limitations. Also, majority of DNA PCR are HIV-1 specific only and same goes for P24 antigen. DNA PCR have more rate of false positives as compared to P24 antigen but PCR is considered more sensitive when compared to P24 antigen test. So, what would give more peace of mind when a person is trying desperately to reach :
a. a negative DNA PCR coupled with a negative antibody test at > 28 days

b. a negative P24 antigen coupled with a negative antibody test at > 28 days
---------Math -Testing Related----------------
Little math for the 2 combinations:

a. DNA PCR at 28 days     - 96%
   ELISA at 28 days       - 75% [conservatively]
   combined sensitivity   - 99%

b. P24 antigen at 28 days - 80%
   ELISA at 28 days       - 75%  [conservatively]
   combined sensitivity   - 95%
-------Math transmission related---------------

vaginal intercourse transmission understanding:
female to male - 1/2000
uncircumcised male -> risk 5 times higher
presence of other STD's quadruples hiv transmission rate - 4x

3 above mentioned factors will make transmission rate  fall to  -> 1/2000 * 5* 4 = 1/200
Let me know your thoughts on this and if you feel that the numbers I put in make any sense to you. I know some people might be tempted to call my ELISA #'s historical from paleolithic age. I jotted them down with extreme conservatism especially for high risk situations.Comments welcomed!
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