Thank you for your inquiry. From what we gather from the question, you were asking about the accuracy of self tests and late seroconversion.
Whole blood self tests have been shown to be more reliable in comparison to oral fluid rapid diagnose tests. However, home tests are overall less reliable than a laboratory test because of the possibility of errors. The test that you described above has reported an accuracy to 99.8%, but any home test has the possibility of instrumental error, as well as user errors associated with incorrect specimen collection (1)(2). For completely conclusive results we recommend a fourth generation test from a health care provider.
Your chances of delayed or late seroconversion are low. Seroconversion is the phase of an infection when antibodies against an infecting agent are first detectable in the blood. During an infection, antigens enter the blood and the immune system makes antibodies in response (3). After 12 weeks of acute infection, you should have antibodies specific to HIV. It is possible for a person to not produce antibodies to HIV but that is in very rare and specific cases of immunodeficient individuals who are unable to make any antibodies. If you were not making any antibodies, the virus would be continuously replicating unchecked and therefore could be detected through an RNA test, or through a test for the p24 antigen. The p24 antigen is a protein associated with the viral capsid or core (4).
A fourth generation test is a combination test that checks for the presence of antibodies AND the p24 protein antigens. p24 antigen is from HIV, and if no antibodies were being made you would be able to detect it because there would be no antibody-antigen complex (4). Notice in the figure below, as the level of antibody increases in the blood, the p24 antigen decreases. A fourth generation test has essentially a zero percent chance of giving a false negative result after 50 days and therefore is the considered the gold standard for HIV testing (5).
As for the symptoms you described, they may be due to many different factors. Due to the fact that the symptoms for acute HIV infection are very broad, I recommend referring to your healthcare provider.
Recommendation: Refer to a health care provider for a confirmatory test.
AIDS Vancouver Helpline/Online, Rashell
If you are satisfied with the Helpline service, please consider donating.
1.) Reliability of HIV Rapid Diagnostic Tests for Self Testing
2.) Autotest VIH
3.) Immunology Basics
4.) p24 Antigen
5.) Probability of a False Negative Result During the Window Period
Figure used (5).