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The earliest test - that can be taken to detect HIV infection is the PCR proviral DNA test. This test can detect the HIV DNA within 15-21 days of the infection.
Polymerase chain reaction (PCR) for proviral DNA (PCR -DNA) can detect proviral DNA during window period, can differentiate latent HIV infection from active viral transcription and can quantitate the copy number of HIV DNA when used with external standards (e.g. viral load assays).
PCR can successfully differentiate between HIV- and HIV-2 infections. Proviral DNA can be detected in peripheral blood mononuclear cells before seroconversion. PCR is also be used to detect HIV infection in neonates born to HIV infected mothers.
The sensitivity of the test is 100% and is very accurate test. You can rely on it.
A proviral DNA PCR - at 27 days post exposure, will be confirmatory and there would be no need to repeat any more tests in the future.