What are Syphilis Tests?
Syphilis tests are laboratory tests used to detect whether the immune system has produced antibodies linked to the infection caused by the bacterium Treponema pallidum, which is responsible for syphilis. Syphilis is a sexually transmitted infection (STI) that can result in affecting multiple organs (skin, genitals, mouth, nervous system, heart, etc.) if left untreated.
Types of Syphilis Test
There are 2 types of Syphilis Tests:
- Non-treponemal tests: The most common tests used to screen and to evaluate response to treatment are the RPR (Rapid Plasma Reagin) and VDRL (Venereal Disease Research Laboratory)
- Treponemal tests: FTA-ABS and TP-PA are used to detect antibodies specific for treponemal pallidum to confirm diagnosis.
It’s important to test for syphilis because many people do not have symptoms in the early stages of infection. Early diagnosis and treatment of the disease can prevent complications of the brain, heart, eyes, and nervous system and reduce transmission to others.
How is the Test Performed?
Syphilis testing usually involves a routine blood collection procedure. The appointment does not require major preparation. The sample collection itself takes only a few minutes.
Preparation
Most people can prepare for a syphilis blood test in the same way as other routine blood tests.
Before collection:
- Fasting is generally not required.
- Continue regular medicines unless your doctor has advised otherwise.
- Tell your health care professional if you have ever been treated for syphilis.
- Wear clothing that gives easy access to your upper arm for the blood draw
- Follow any instructions given to you by your health care provider
Some antibodies to syphilis may persist in the blood even after successful treatment, so it is useful to know about previous infection or treatment.
Collection
Blood is drawn from a vein, usually one in the arm.
At the time of collection:
- The skin is disinfected by treatment with an antiseptic
- A small amount of blood is collected using a sterile needle
- Sample is dropped into right SST collection tube
- Pressure is applied to the area after removal of the needle.
- It usually takes only a few minutes to perform and causes minimal discomfort.
More samples may be needed in some medical situations. For example, if the doctor suspects that there is involvement of the nervous system, they may consider testing cerebrospinal fluid (CSF).
Laboratory Testing
The collected blood sample is tested for antibodies against Treponema pallidum. Screening often begins with either a non-treponemal test or a treponemal test, depending on the laboratory protocol. After a positive screening result, the laboratory performs additional confirmation testing. The final interpretation is made by considering the laboratory findings together with clinical information.
What are the Symptoms that Prompt this Test?
Syphilis does not always cause obvious symptoms. In many cases, the early symptoms are mild or not recognizable. This is why testing is often recommended after possible exposure, even if you feel healthy.
You may be referred for a test for syphilis if you experience the following symptoms:
- A painless sore (chancre) on or near the mouth, genitals, or anus
- Skin rash, especially on the palms or the soles
- Swollen lymph glands
- High fever
- Throat pain
- Fatigue
- Pain in muscles
- Fine, spotty hair loss
- Migraine/headaches
- Losing weight without trying
If the infection is not treated, later symptoms can include involvement of other parts of the body such as:
- Changes in sight or hearing
- Difficulty with balance or coordination
- Problems with memory
- Numbness or weakness
- Complications affecting the heart or nervous system
Testing may also be advised for people who have had contact with someone diagnosed with syphilis, individuals undergoing STI screening, and pregnant women as part of routine antenatal care.
What are Normal Ranges for These Tests?
Syphilis tests are not interpreted using a standard numerical reference range like many blood tests. Instead, laboratories report whether antibodies related to Treponema pallidum have been detected.
Results are generally reported as:
- Negative or Non-reactive: No evidence of syphilis infection was detected.
- Positive or Reactive: Antibodies associated with Treponema pallidum infection were detected.
- Equivocal or Indeterminate: Additional testing may be required to confirm the result.
For non-treponemal tests such as RPR or VDRL, results may also be reported as titres, which help healthcare providers monitor treatment response over time
“The reference ranges vary depending on the laboratory and the methodology used. Individuals must consult their healthcare provider for correct interpretation of the results.”
What Do Positive Results Indicate?
Positive results may indicate:
- Active syphilis infection
- Previous treated syphilis infection
- Early-stage syphilis
- Latent syphilis
- Congenital syphilis
- Neurosyphilis or other advanced forms of the disease
Additional testing may be required to determine the stage of infection and guide treatment decisions.
What Do Negative Test Results Indicate?
Negative results usually mean that infection with syphilis is not likely. False negative results, however, may occur if:
- Testing occurs very soon after exposure.
- The body has not yet produced detectable antibodies.
- The infection is in its early stages.
If recent exposure is suspected, your healthcare provider may recommend repeat testing after several weeks.
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