Thank you for your question.<\/p>\n
I am assuming you are writing from the UK? Therefore I will answer as if you are and if I am wrong you will have to let me know.<\/p>\n
The time at which a test is conclusive depends on the type of test you have. If you have a fourth generation test which checks for antigens and antibodies then it will detect 95% of infections at 28 days and is conclusive at 90 days. Some clinics still operate on old policies for third generation tests which only look for antibodies and so would require a test between 6-12 weeks for it to be conclusive.<\/p>\n
You mention that you are planning to work abroad but you did not say which country or for how long. Different countries have different policies on HIV testing. Without knowing which country you are going to it is hard for me to explain why they are asking for 2 tests. In general countries with free healthcare are reluctant to treat HIV in visitors due to the cost of treatment.<\/p>\n
It is possible they are asking for two certificates to rule out the possibility of a false negative which could occur during the window period. False negatives are more likely to occur with third generation tests as it takes longer to make antibodies than for antigens found on the surface of the virus to be detected.<\/p>\n
Immigration laws and policies regarding HIV testing are individual for each country and unfortunately you have to abide by these rules and produce any documentation they require.<\/p>\n