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 3 months post contact and will have accurate general testing from 4 weeks. Therefore it is always advisable to have repeat full testing at 3 months post the last unprotected contact before engaging in unprotected intercourse with another partner.
“Using the 4th Generation HIV test (these test for antibodies and P24 antigen) the tests will detect the great majority of individuals who have been infected with HIV at one month after a specific exposure. An additional HIV test should be offered to all persons at 3 months to definitively exclude HIV infection”. (BASHH-British Association of Sexual Health and HIV).
For clients presenting from 28 days after exposure, we would recommend the HIV Duo test, a 4th generation assay, which is the gold standard HIV test and is highly accurate from a month.
We also offer the Early HIV/STD screen for those clients who present before 28 days. This test will pick up the majority of cases from 10 days for HIV.
For both the HIV Duo test and the Early HIV/STD Screen, we would advise a repeat test at 3 months for definite results.
For clients presenting from 3 months, testing can be via the HIV Duo test or the Insti HIV test, which tests for HIV 1 and 2 antibodies. Both tests are conclusive from this point.
Chlamydia and Gonorrhoea Testing
“Recommended Clients should have chlamydia testing when they present with NAAT testing. But we should 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 20th May 2008)
CityDoc uses NAAT testing as standard for all urine based Chlamydia/Gonorrhoea testing. The test is conclusive at 14 days post contact.
We use the highly accurate IgG/IgM antibody test for test as recommended by BASHH.
IgM is detectable towards the end of the second week of infection while IgG is detectable in the fourth or fifth week.
Repeat screening at 3 months post infection is recommended for a conclusive result.
Hepatitis C testing
CityDoc now tests routinely using hepatitis C antigen rather than hepatitis C antibody in its general screens. Hepatitis C antigen is present well before the occurrence of antibodies and can be accurately detected from as early as 10 days.
We advise repeat testing at 3 months as part of a general repeat screen given the variation between individuals in terms of the window period.
Hepatitis C can also be accurately detected from 10 days after exposure by PCR (DNA) testing using the Early STD screen.
Hepatitis B testing
For routine sexual health screening we screen for hepatitis B antigen directly. This is accurate from 4 weeks but conclusive from 3 months post contact.
Early testing from 10 days
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.
This test has reduced the window period for HIV testing from 16 days to 6 months with conventional testing to 7-10 days.