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Finding the right tests…
Serology
VDRL checks your blood for antibodies your body makes in response to the cell damage syphilis causes, rather than antibodies aimed at the bacterium itself. This is why it's called a nontreponemal test — a distinction that matters, because these antibodies can also show up with other infections, autoimmune conditions, pregnancy, or older age, giving an occasional false positive unrelated to syphilis. VDRL usually comes first as a screening step, and a reactive result is typically followed by a treponemal test such as TPHA to confirm the diagnosis. Its titre, a measure of how strong the reaction is, tends to fall after successful treatment, which is why VDRL is also used to track whether treatment is working.
This test reports whether VDRL antibodies are present in your blood, usually as a titre — a dilution number showing how strong the reaction is — rather than a simple positive or negative. A meaningful change in titre is generally a fourfold shift, such as from 1:4 to 1:16, used to judge whether an infection is worsening or treatment is working. A reactive result alone doesn't confirm syphilis, since several unrelated conditions can cause a false positive, so it's usually followed by a treponemal confirmatory test. A single blood sample is enough, with no preparation needed.
VDRL looks for antibodies your immune system makes against substances released by cells damaged during a syphilis infection, rather than antibodies that target the syphilis bacterium directly. Because these antibodies aren't specific to syphilis, other conditions — including some autoimmune diseases, other infections, pregnancy, and older age — can occasionally trigger a reactive result even without syphilis being present, known as a biological false positive.
VDRL's advantage is that it's simple and inexpensive to run, which is why many labs still use it as the initial screen. A reactive VDRL is typically followed by a treponemal test, such as TPHA, that specifically targets the syphilis bacterium, confirming whether the reactive result reflects a genuine infection.
Unlike treponemal tests, VDRL titres generally fall after successful treatment and can eventually become nonreactive, which is why doctors repeat it over time to check that treatment is working. A titre that keeps falling is reassuring, while one that fails to drop as expected, or rises again, can prompt your doctor to look for treatment failure or reinfection.
Yes. CDC guidance notes that conditions unrelated to syphilis, including some autoimmune diseases, other infections, pregnancy, and older age, can occasionally cause a reactive VDRL result, known as a biological false positive.
VDRL looks for antibodies linked to general cell damage from syphilis and can occasionally react to unrelated conditions, while TPHA targets the syphilis bacterium directly and is used to confirm a reactive VDRL.
The titre shows how dilute your blood can be before the antibody reaction stops showing up; a higher number generally reflects a stronger reaction, and your doctor watches for a fourfold change to judge whether things are improving or worsening.
Often, yes. VDRL titres generally fall after successful treatment and can eventually become nonreactive, which is why it's used to track treatment response, unlike treponemal tests such as TPHA.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
Because VDRL isn't specific to syphilis, a reactive result needs confirming with a treponemal test such as TPHA before syphilis is diagnosed.
Yes, VDRL or a similar nontreponemal test is commonly included in antenatal screening, since untreated syphilis in pregnancy can affect the baby.
No. No special preparation, including fasting, is needed before this blood draw.