What it measures
Antibodies to Treponema pallidum, the bacterium that causes syphilis. This is the usual screening test for syphilis. The antibodies usually stay positive for life after an infection, even once it has gone.
Why people test it
- Part of routine sexual health screens, and checks after a new partner.
- Tested when a painless sore, a rash or other symptoms suggest syphilis.
- Part of the infection screening offered in pregnancy.
Typical range
Reported as reactive or non-reactive (positive or negative), and a reactive result is followed by further tests, such as RPR, to tell a current infection from a past one. Methods vary between labs, and your report shows how the lab reads the result.
Finger-prick or vein?
A blood test. Finger-prick kits and vein draws are both offered.
Sexual Health Oxfordshire, an NHS service, gives 4 weeks after possible contact as the wait before a syphilis blood test, with a further test at 3 months in some cases.