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| RPR test |
What is a rapid plasma reagin (RPR) test?
A rapid plasma reagin (RPR) test is a
blood test used to screen you for syphilis. It works by detecting the
nonspecific antibodies that your body produces while fighting the infection.
Syphilis is a sexually transmitted
infection (STI) caused by the spirochete bacterium Treponema pallidum.
It can be fatal if left untreated.
Combined with specific antibody testing,
the RPR test allows your doctor to confirm the diagnosis of active infection
and start your treatment. This reduces the chances of complications and the
spread of the disease by an infected but unaware person.
When is an RPR test recommended?
Your doctor may order an
RPR test for several reasons. It’s a quick way to screen those at high risk for
syphilis. Your doctor may also order this test if you have syphilis-like sores
or a rash. Doctors also routinely screen pregnant women for syphilis using an
RPR test.
States used to require
that people who are applying for a marriage certificate get a screening test
for syphilis. The only state that still requires a blood test of any type is
Montana, and a syphilis test is no longer included.
The RPR test measures
antibodies that are present in the blood of someone who has syphilis, rather
than the bacterium that causes the disease. It can also be used to check the
progress of treatment for active syphilis. After a course of effective
antibiotic therapy, your doctor would expect to see the number of antibodies
drop, and an RPR test could confirm this.
How is blood for the RPR test obtained?
Doctors obtain blood
for the RPR test with a simple procedure called a venipuncture. This can be
done in your doctor’s office or a lab. You don’t need to fast or take any other
special measures before this test. The test involves
the following steps:
1. A healthcare provider will ask you to sit in a comfortable chair or lie
down on a cot or a gurney.
2. They then tie rubber tubing around your upper arm to help make your veins
stand out. When they find your vein, they will swab the spot with rubbing
alcohol to cleanse it and insert a needle into the vein. The needle may produce
a sudden, sharp pain, but it typically doesn’t last long.
3. Once they have the blood sample, they’ll remove the needle from your vein,
hold pressure on the puncture site for a few seconds, and offer you a bandage.
Risks of the RPR test
Venipuncture is
minimally invasive and carries very few risks. Some people complain of
soreness, bleeding, or bruising after the test. You can apply an ice pack to
the puncture wound to help relieve these symptoms.
Some people may become
light-headed or dizzy during the test. Tell the healthcare provider if your
dizziness lasts longer than a few minutes.
Understanding your results
A normal RPR blood
sample shows no antibodies typically produced during an infection. However,
your doctor cannot completely rule out syphilis if they see no antibodies.
Once you’ve been
infected, it takes some time for your immune system to create antibodies.
Shortly after infection, a test may not yet show any antibodies. This is known
as a false negative.
False negatives tend
to be more common in the initial and end stages of infection. Among people who
are in the secondary (middle) stage of infection, the RPR test result is nearly
always positive.
The RPR test also can
produce false-positive results, suggesting you have syphilis when you actually
don’t. One reason for a false positive is the presence of another disease that
produces antibodies similar to the ones produced during a syphilis infection. A
few of the conditions that can cause a false positive include the following:
- HIV
- Lyme disease
- malaria
- lupus
- certain types of pneumonia, especially those
associated with a compromised immune system
If your result is
negative, your doctor may ask you to wait a few weeks and then return for
another test if you’re at a higher risk for syphilis. This is because of the
RPR test’s potential for a false negative.
Due to the risk of
false-positive results, your doctor will confirm the presence of syphilis with
a second test, one that is specific for antibodies against the bacterium that
causes syphilis, before starting your treatment. One such test is called
the fluorescent treponemal antibody-absorption (FTA-ABS) test.
Follow-up after the RPR test
Your doctor will start
you on antibiotic treatment, usually penicillin injected into the muscle, if
your RPR and FTA-ABS test both show signs of syphilis. New infection usually
responds to treatment quickly.
At the end of treatment, your doctor will most likely recommend that you
get another RPR test to make sure your antibody levels are dropping.
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