Syphilis, a sexually transmitted disease (STD) caused by the bacteria Treponema pallidum, can be detected via blood tests. However, as there are various syphilis blood tests available commercially, you may find it daunting to choose the right one.
Read further to get more guidance about the different serological tests for syphilis.
There are two primary categories of serological syphilis tests: the nontreponemal test and the treponemal test. While a nontreponemal test is often included in many STD screening tests, treponemal tests are requested to confirm syphilis.
Both types of syphilis blood tests are essential for diagnosis. You will have to take more than one test (usually one of each type), for your healthcare provider to detect syphilis, determine its stage, and assess its severity.
Below are syphilis blood tests identified under these two types.
Nontreponemal tests measure the reactivity of the blood sample to an antigen which may suggest T. pallidum infection. To do this, the procedure screens for antibodies that may not be specific to syphilis but can still trigger the condition.
Therefore, nontreponemal tests are considered the first line of a diagnostic test for syphilis – regardless of whether symptoms have appeared.
The most common nontreponemal test for syphilis is the rapid plasma reagin (RPR) blood test and venereal disease research laboratory (VDRL) test.
The RPR blood test uses reagin as the antigen and is deemed more reactive than VDRL. In addition, a VDRL test requires a microscopic examination of the blood sample, while an RPR test does not need such a process.
Treponemal serological tests detect proteins specific to syphilis. As T. pallidum gets into the system, your immune system produces antibodies to fight it off. Treponemal testing is, therefore, a confirmatory test for syphilis.
However, these antibodies may stay in circulation even after a syphilis treatment. Consequently, it’s not used for monitoring whether the treatment was successful.
While a nontreponemal syphilis test usually precedes a treponemal test, there are instances where it goes the other way around. This method is referred to as reverse sequence testing. Nevertheless, multiple testing, regardless of order, is essential for accurate diagnosis.
Some of the most common types of treponemal syphilis blood tests included the following:
The FTA-ABS blood test and TPHA test are the most common treponemal test, usually taken with either RPR or VDRL. They are also prescribed for pregnant women and if you have been diagnosed with other STDs.
Detecting syphilis a week or two after the lesions appear ensures swift and effective treatment. However, in most cases, the test is taken under specific circumstances. You will have to take a syphilis lab test as required for the following:
Without a blood test, syphilis may be hard to detect. Its symptoms can mimic those of other conditions. As a result, it’s easy to misidentify or ignore the signs altogether. It’s also why it earned the nickname “The Great Pretender”.
Syphilis is divided into various stages: primary, secondary, and latent. It is during the secondary stage that symptoms appear most prominently.
Syphilis enters its primary stage after infection, characterized by round, firm, and painless chancres. These chancres may develop in inconspicuous areas like the anus or vagina. While they may go away on their own, without treatment, they could recur and develop into the secondary stage.
At the secondary stage, the following symptoms become prominent.
These symptoms can also be healed without treatment. However, you’re risking further development of the infection, making it proceed to the latent stage. In addition, you risk transmitting the disease to your sexual partner/s.
During the latent stage, syphilis symptoms get suppressed, but the causative pathogen stays with you for a while. The most significant danger of latent stage syphilis is that it could spread and cause permanent damage to your brain, heart, liver, blood vessels, bones, joints, eyes, and nerves.
As syphilis is transmitted via oral, vaginal, and anal sex, those who are active sexually ought to use proper protection. Plus, they should also undergo STD testing that covers not just syphilis but other common STDs, like chlamydia, gonorrhea, and herpes.
In addition, pregnant women who have syphilis are also at risk of premature labor, miscarriage, and stillbirth in fetuses.
In fact, the Centers for Disease Control and Prevention (CDC) reports about 40% of babies born to mothers with untreated syphilis die as a result of the infection. Others survive but develop conditions like nerve damage, severe anemia, bone damage, and skin disease.
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Screening and diagnosing syphilis require multiple tests. While serological tests for this STD provide precise data, a combination of treponemal and non-treponemal blood tests ensure accuracy. Your doctor may order RPR and VDRL for screening, then FTA-ABS for verifying the condition further.
An RPR is more sensitive than VDRL, especially during the middle stage of the infection – approximately four to six weeks after T. pallidum has gotten into your system. In addition, RPR is considered easier to use than VDRL.
Nonetheless, both tests screens for antibodies produced in response to syphilis infection. However, they can also be non-specific to the condition, which is why a treponemal test is needed.
The ideal time to take a syphilis antibody test is one to three weeks after the lesions or chancres appear. Or, you could take it around six weeks after being exposed to someone with confirmed syphilis. Timing is crucial when going through a blood test for screening, as getting tested too early can lead to false negatives.
Urine tests for syphilis detection are not available commercially. Despite some STD kits only needing urine for examination, syphilis typically requires a blood test. It’s far more effective and straightforward as far as identifying antibodies goes.
You can buy at-home kits for syphilis detection, where you will be required to collect blood samples via the finger prick method. You will be directed to send the sample to a laboratory where only professionals can perform analysis.
But although at-home test kits are convenient, a blood test performed in a medical laboratory still provides more accurate results. For one, the blood sample collection is done in a sterile environment, and the analysis method is more sensitive.
The likelihood that you will need a syphilis test is determined by your sexual activity, and the presence of syphilis sores, among other factors. If you’re taking a routine STD screening, consider taking non-treponemal tests like the RPR blood test. If you tested positive for syphilis, take treponemal serological tests like FTA-ABS and agglutination assay for confirmation.
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