When to Test? Accuracy Sexual Health Testing
There is no hard scientific evidence to quote exact accuracies of each test following a specific contact. The window period, which is the period between infection and time when a test can reliably detect the condition will vary between individuals.
As a general rule the vast majority of people will have infection excluded for STDs at 12 weeks post contact and will have accurate general testing from 45 days. Therefore it is always advisable to have repeat full testing at 12 weeks post the last unprotected contact before engaging in unprotected intercourse with another partner.
The 4th Generation HIV test (these test for antibodies and P24 antigen) will detect if individuals are infected with HIV from 45 days after a specific exposure. Evidence by BASHH (2020) Adult HIV testing guideline found 99% of HIV infections would be identified by 4th generation tests by 45 days post-exposure. An additional HIV test should be offered to all persons at 12 weeks to definitively exclude HIV infection (BASHH-British Association of Sexual Health and HIV 2020).
For clients presenting from 45 days after exposure, we would recommend Citydoc HIV Duo test, a 4th generation assay, which is the gold standard HIV test and is highly accurate.
We also offer the Early HIV screen for those clients who present before 45 days. This test will pick up the majority of cases from 10 days for HIV.
For clients presenting from 12 weeks, testing can be via the HIV Duo test or the instant HIV finger prick which tests for HIV 1 and 2 antibodies. Both tests are conclusive from this point.
Chlamydia and Gonorrhoea Testing
Citydoc provides NAAT testing for chlamydia and Gonorrhoea.. We advise clients who present less than two weeks post their last contact that they should repeat the NAAT test two weeks after the last exposure (BASHH 2018).
We use the highly accurate IgG/IgM antibody test. IgM is detectable towards the end of the second week of infection while IgG is detectable in the fourth or fifth week. Depending on the sexual risk repeat screening is recommended between 6- 12 weeks post contact contact and at 12 weeks this would be a conclusive result (BASHH 2019).
Hepatitis C testing
CityDoc screens for hepatitis C antibody in its general screens detectable from 6-9 weeks.
We advise repeat testing at 12 weeks as part of a general repeat screen given the variation between individuals in terms of the window period.
Hepatitis B testing
For routine sexual health screening we screen for hepatitis B antigen directly. This is accurate from 4 weeks but conclusive from 12 weeks post contact.
Early testing from 10 days
In select nationwide clinics we use PCR (DNA) testing to allow accurate testing from as early as 10 days post contact using the STDX blood test. It detects HIV type 1, HIV type 2 and Hep C (RNA) and Hep B DNA.
The test does not discriminate which virus is in a specimen. Results are reported as Detected or Not Detected. Those samples, which have positive findings then undergo further reflect confirmatory testing to confirm the viral target identity.