The Rapid Plasma Reagin Test for Diagnosing Syphilis

The rapid plasma reagin test is similar to a conventional blood test, so it has little risks. Today's article will explain what it consists of and its uses.
The Rapid Plasma Reagin Test for Diagnosing Syphilis

Last update: 09 August, 2021

The simple rapid plasma reagin test can detect syphilis antibodies through a blood sample. In fact, it’s been an important advance in the control of this disease in recent years.

Syphilis is a sexually transmitted infection caused by a bacterium called Treponema pallidum. There is a treatment for it. However, it’s still a major cause of mortality.

This disease is highly contagious because many people who have it are ignorant of it. Today’s article will explain what the rapid plasma reagin test consists of and how it helps detect it.

What’s syphilis?

Syphilis is a sexually transmitted disease caused by a spirochete-type bacterium called Treponema pallidum, as mentioned above. This infection transmits through contact with infectious sores on the genitals, rectum, anus, and even the mouth.

People can transmit it through blood infusions and women can also pass it on to their babies during pregnancy. The stages are symptomatic and it makes the diagnosis more complex.

Primary syphilis occurs shortly after infection. There may be fever, muscle aches, malaise, and swollen lymph nodes at this stage. Also typical is a lesion called a chancre, an ulcer through which the infection passes on.

The ulcer is painless and people seldom notice it. Thus, it’s precisely when the asymptomatic period begins if there’s no treatment. Furthermore, syphilis remains latent and continues to spread.

Damage occurs in all organs as the years go by. It can lead to blindness, paralysis, numbness, and even death. This is why it’s important to diagnose it early. Actually, treatment is simple and effective but people must start it as soon as possible.

The syphilis bacteria.
The bacterium that causes syphilis is a spirochete, named after its shape.

Find out How Can Women Protect Themselves from STDs?

The rapid plasma reagin test

This test detects specific antibodies in the blood. Those the body synthesizes against substances in other cells damaged by the bacterium Treponema pallidum.

In other words, the bacterium attacks the body’s cells in the first instance. These secrete substances for which the immune system synthesizes specific antibodies when damaged. However, the antibodies only appear when people are already undergoing treatment.

The rapid plasma reagin test helps identify active syphilis. However, it isn’t definitive even though it does guide the diagnosis. A doctor can then order other tests if this one detects antibodies.

This test is also used to study the progress of the disease after beginning therapy. The antibodies in the blood decrease and it means the treatment works. Also, the rapid plasma reagin test is mainly a screening test in sexually active people.

Rapid plasma reagin test and pregnancy

A mother can transmit syphilis to her fetus during pregnancy and it poses many risks to the baby. In fact, it increases her likelihood of miscarriage.

This is why some countries require a rapid plasma reagin test to detect the infection during pregnancy. The test isn’t part of the protocol in some places but a doctor will do it if they detect any risk factors in the mother.

The rapid plasma reagin test

This test is similar to a conventional blood test. The first step is to draw blood from the patient’s so the technician ties a small elastic band around the arm — to find the vessel.

They then wipe the skin with an antiseptic and insert a small needle into the area selected for the puncture. The sample doesn’t have to be large so a small tube is usually enough.

Then, they send the blood to a lab that can perform the test. This entire procedure doesn’t require any prior preparation.

Interpreting the results

The rapid plasma reagin test can produce different results. It’s normal or non-reactive when there are no syphilis antibodies in the blood according to specialists at San Diego Health.

However, this requires certain considerations. A negative test result doesn’t completely rule out syphilis. This is because infected people don’t produce antibodies in the early stages of the disease.

There may even be antibodies at a low titer, but they’re usually undetectable. Thus, several months may go by before a person realizes they have the disease.

It’s also possible that, just after treatment, the rapid plasma reagin test fails to detect the antibodies. It’s, therefore, recommended to repeat the test after a couple of weeks.

In addition, the best time to do the test is in the middle stages of syphilis. That is, once enough time has gone by for the body to generate antibodies but before treatment.

The results of the rapid plasma reagin test are influenced by other infections. There are certain pathologies in which syphilis-like antibodies synthesize. For example, malaria, HIV, Lyme disease, and lupus.

Antigens attacking viruses.
Measuring antibodies has a margin of error. Some diseases produce similar responses in the body that laboratory tests fail to detect.

Is the test risky at all?

The rapid plasma reagin test is simple and safe. However, there are some small risks involved in taking a blood sample. For example, bleeding at the puncture site, bruising, and dizziness.

Infections are unlikely to occur. What you must keep in mind is the test isn’t exclusive for syphilis and may have false negatives/positives. This is why additional tests must confirm the diagnosis.

One of the tests to confirm it is the fluorescent treponemal antibody absorption test (FTA-ABS). It looks for antibodies to syphilis more specifically.

Syphilis must be detected early

The thing to remember about the rapid plasma reagin test is it’s an initial screening test for syphilis. It identifies antibodies to the infection but doesn’t have as much specificity.

Thus, additional tests are usually required for confirmation after a positive result. In addition, the result might be negative, but the clinical suspicion is high. Thus, it may also be necessary to repeat the test or include a different test if so.

The rapid plasma reagin test is still very useful, however. The reason is syphilis is a highly contagious but treatable infection. This is why early detection and treatment can help prevent serious complications.

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