Syphilis Blood Tests and How Results Are Interpreted

Testing at our clinic

We ask when possible exposure occurred, whether you have a lump, sore or rash, and whether you have previously been tested or treated for syphilis. Examination is limited to what is clinically necessary and is explained before it is performed.

A blood sample is taken from a vein. RPR and a Treponema pallidum-specific antibody test are generally measured together, with quantitative results used when clinical evaluation or follow-up is required. Tests sent to an external laboratory are not finalized on the same day.

What the two tests mean

• RPR is a nontreponemal test. It helps assess disease activity and change after treatment, but it can also be reactive for reasons other than syphilis.
• The treponemal antibody test is more specific for exposure to Treponema pallidum. It often remains reactive after successful treatment and is not used alone to judge treatment response.

How result combinations are interpreted

• RPR nonreactive / treponemal antibody nonreactive: no antibody is detected at present, but very early infection is still possible.
• RPR reactive / treponemal antibody reactive: active infection or antibodies remaining after previous treatment are possible; history, symptoms, quantitative RPR and change over time are needed.
• RPR nonreactive / treponemal antibody reactive: previous treated infection or early infection may be present; previous treatment and recent exposure are reviewed and repeat testing may be needed.
• RPR reactive / treponemal antibody nonreactive: a biologic false-positive RPR or early infection is possible; the result is reassessed rather than interpreted from one sample alone.

Testing after a recent exposure

Antibodies may not yet be detectable immediately after infection. Japanese guidance recommends considering repeat RPR and treponemal antibody testing at about four weeks after the possible exposure when syphilis is still suspected despite an initial negative result.

Do not wait four weeks if you have a suspicious sore or rash, your partner has been diagnosed with syphilis, or you are pregnant or may be pregnant. Seek an assessment promptly.

Follow-up after treatment

The pretreatment quantitative RPR value is used as the baseline. Symptoms and RPR are followed using the same test method when possible. Japanese guidance recommends measuring RPR and treponemal antibody at approximately four-week intervals initially.

A substantial RPR decline supports treatment response: approximately one half of the pretreatment value with an automated method, or one quarter with a twofold serial-dilution method. The pace of decline varies, and a treponemal antibody may remain reactive after cure, so follow-up is individualized and may continue for up to a year.

When specialist care is needed

Visual symptoms, hearing loss, severe headache or neurologic symptoms, pregnancy, or results that do not match the clinical findings may require prompt referral to an appropriate specialist or obstetrics and gynecology service.

Authoritative information