Syphilis Testing: Understanding Your Report

Section Editor: Rodney E. Rohde PhD
June 4, 2026

Syphilis is a sexually transmitted infection caused by a bacterium called Treponema pallidum. A bacterium is a microorganism, a living thing too small to see without a microscope. Syphilis develops in stages and, if it is not treated, can affect many parts of the body over time, but it can be cured with antibiotics. Testing for syphilis usually uses two different blood tests together, because each one has limitations, and the results often come in pairs that can seem to disagree.

This article explains the two types of syphilis blood tests, how they are combined, and what the wording on your report means, so you can better understand a report you have received.

What is syphilis, and why are two tests used?

Syphilis usually begins with a painless sore (the primary stage), and can later cause a rash and other symptoms (the secondary stage). It may then enter a hidden stage with no symptoms at all, and, if still untreated, can cause serious problems in later stages. It can also be passed from a pregnant person to their baby. At every stage, syphilis can be cured with antibiotics.

Because Treponema pallidum cannot be easily grown in the laboratory, the way many other bacteria can, syphilis is usually diagnosed with blood tests that detect antibodies, the proteins the immune system makes in response to the infection. Two different kinds of antibody tests are used together, because each answers a different question and neither is enough on its own.

The two types of blood tests

Non-treponemal tests (RPR or VDRL) — These detect antibodies to substances released when cells are damaged by the infection, rather than antibodies against the bacterium itself. The result is reported as a titer, a number such as 1:8 or 1:32 that reflects how much antibody is present. The titer tends to rise during an active infection and fall after successful treatment, making these tests useful for monitoring. Their drawback is that they can sometimes be positive when there is no syphilis, for example, during pregnancy, with some autoimmune conditions, or with certain other infections, so a positive result needs to be confirmed.
Treponemal tests (such as TPPA, FTA-ABS, or automated immunoassays) — These detect antibodies aimed specifically at Treponema pallidum, so they are more specific and are used to confirm that an antibody result truly reflects syphilis. Their drawback is that they usually stay positive for life, even after the infection has been cured. For this reason, a treponemal test cannot tell a current infection from a past, treated one, and it is not used to monitor treatment.

How the tests are combined

Because each test has limitations, laboratories use them together, in one of two orders:

The traditional order — A non-treponemal test (RPR or VDRL) is performed first, and if it is reactive, a treponemal test is performed to confirm the result.
The reverse order — A treponemal test is done first, which is easier for laboratories to automate, and if it is reactive, a non-treponemal test is done to see whether the infection appears active. If the two tests disagree, a second, different treponemal test is done to settle the question.

This is why your results often appear in pairs, and why a single positive test is not the whole story.

How to read your result

The combinations below cover the most common patterns. Your doctor interprets them along with your history and any symptoms.

Both tests reactive (treponemal and non-treponemal positive) — Active syphilis is likely. This may be a new, untreated infection or one that was treated very recently, and the non-treponemal titer helps show how active it is.
Treponemal positive, non-treponemal negative — This common pattern usually means a past syphilis infection that has been treated, or sometimes a very early or a late infection. A second treponemal test may be used to confirm it. It does not necessarily mean you have an active infection now.
Non-treponemal positive, treponemal negative — The treponemal test did not confirm syphilis, so the non-treponemal result is most likely a false positive from another cause.
Both tests negative — Syphilis is unlikely, although a very recent infection can be missed if testing was done too early.

What the titer means and how treatment is monitored

The non-treponemal titer, such as 1:8 or 1:32, is followed over time, with a higher number indicating more antibody. After successful treatment, the titer is expected to fall, and a fourfold drop, for example, from 1:32 to 1:8, is the usual sign that treatment has worked. A fourfold rise can indicate a new infection (reinfection) or that treatment did not fully work. The treponemal test is not used in this way because it usually stays positive regardless of treatment.

Other tests

In early syphilis with a visible sore, the bacterium can sometimes be detected directly in a sample taken from the sore, using a special microscope or a molecular (PCR) test, as described in the article on PCR, antigen, and antibody tests. If there is concern that syphilis has affected the nervous system, testing of the fluid around the brain and spinal cord, obtained through a procedure called a lumbar puncture, may be done.

What happens after these tests

Syphilis testing describes what was found, and it informs the decisions you and your healthcare team make together rather than dictating them on its own.

A confirmed syphilis infection is treated with antibiotics, usually penicillin, which cures the infection. After treatment, your non-treponemal titer is followed to confirm that the infection is responding. Syphilis is reportable to public health authorities, who can help with notifying and testing partners so that they can be treated as well. Testing for syphilis is also a routine part of pregnancy care, because the infection can pass to the baby, and treatment prevents this.

Questions to ask your doctor

Which syphilis tests did I have, and what did each one show?
Based on both tests, do I have an active infection, a past one, or none?
My treponemal test is positive but my RPR is negative. What does that mean for me?
Could my result be a false positive, and is a confirmatory test needed?
What is my titer, and what will it tell us over time?
If I have syphilis, what does treatment involve, and will it cure the infection?
How and when will we check that treatment has worked?
Should my partner or partners be tested and treated?
If I am pregnant, what does this mean for my baby?
Who should I contact with questions about my results or treatment?