Syphilis is a sexually transmitted disease (STD) caused by the bacterium Treponema pallidum. Tests for syphilis can be either treponemal (identifying an antibody that occurs specifically in T. palliduminfection ) or nontreponemal (identifying a nonspecific antibody that is present in a variety of infectious diseases, including syphilis). Treponemal tests include the fluorescent treponemal antibody-absorbed double stain test (FTA-ABS DS) and the microhemagglutination-T. pallidum test (MHA-TP). The most common diagnostic tests used to diagnose syphilis are the nontreponemal tests called the rapid plasma reagin test (RPR) and the Venereal Disease Research Laboratory test (VDRL). These two tests are both reagin flocculation tests used to verify that an antigen-antibody reaction has occurred.
Syphilis tests can be used to screen for the disease in sexually active young adults and other high risk groups, pregnant women, patients requiring premarital examinations, and blood donors. Syphilis tests also are used to diagnose the disease when the patient has symptoms indicative of the disease. These symptoms can include a single genital ulcer (chancre), a reddish brown rash, and swollen lymph glands. RPR and VDRL tests are initial screening tests for syphilis and positive results are confirmed with more sophisticated tests. Of the two tests, RPR testing is more common.
The RPR and VDRL tests are nontreponemal tests, meaning that they do not identify the bacterium or the antibodies unique to syphilis. These tests indicate the presence of reagin antibodies. Reagin is a nonspecific type of antibody that can occur during many types of infection other than syphilis. Since these tests are only initial screening tests, the more sophisticated treponemal tests must be used to confirm the diagnosis.
As with all venous blood samples taken from the inner crease of the arm, special precautions should be taken for compromised patients. Health care providers should avoid drawing a blood sample from the arm that also has an intravenous line, is edematous, or has scar tissue, an existing hematoma, or damaged veins. As with all blood samples or body fluid collections, health care providers should use standard precautions to protect themselves and others from exposure to the potentially infectious samples or equipment used to obtain the samples.
Biological false-positive results
There are many conditions that can cause a false-positive test result when a patient is tested for syphilis with RPR or VDRL tests. Conditions that can produce a reactive test result include:
- chicken pox
- infectious mononucleosis
- lupus erythematosus
- pnemococcal pneumonia
- rheumatic fever
- rheumatoid arthritis
In 1999, the Centers for Disease Control documented over 35,000 cases of syphilis reported in the United States. Although on the decline in recent years, syphilis remains a serious sexually transmitted disease that can lead to organ damage and eventual death if left untreated. Treatment cures the infection, but cannot reverse damage already done. While transmission is primarily through sexual contact, a mother can transmit the disease to her fetus. After the bacterium enters the body, the organism incubates for several weeks. After that time, the disease can progress through additional distinct stages over several years if not treated. The four stages of syphilis are:
- Primary stage (about 21 days after contact): chancre on an area that has contacted an infected person, like the penis, vagina, anus, or mouth; swollen lymph glands in the groin area.
- Secondary stage (about 4–8 weeks after the chancre appears and heals): sore throat , low fever, tiredness, weight loss, skin lesions, reddish brown rash especially on bottoms of feet and palms of hands.
- Latent stage (after the passing of the first secondary attack): no clinical signs evident and cerebrospinal fluid is normal; this stage may last for several months or years or for the remainder of the patient's life.
- Late (or Tertiary) stage (1–10 years after initial infection): destructive stage; cardiovascular system and central nervous system attacked; skin or organ tumors, paralysis , madness, blindness, sometimes death.
Because syphilis is a serious yet curable disease that can be transmitted to others, it is important that potentially infected patients be tested. The two most common tests are the RPR and the VDRL test, both of which test blood for antibodies the immune system produces in response to a variety of infections, including syphilis. The blood sample is obtained through simple venipuncture. The RPR and VDRL tests mix a sample of the patient's blood with a lipid antigen. If reagin antibodies are present in patient's blood, a clumping reaction (flocculation) occurs between the antibody and the antigen. However, the body creates reagin antibodies in a variety of conditions other than syphilis infection, and the test can appear reactive (or positive) when the patient does not have syphilis.
The RPR test uses a charcoal emulsion of cardiolipin to detect reagin antibodies. With a blunt needle, the antigen is placed into the center of a small circle on a plastic-coated card. Then, a small sample of the patient's serum is added to the circle and mixed with the antigen. The card is mechanically rotated at room temperature for eight minutes and the suspension is examined for visible clumping, which indicates a positive test. Generally, a positive result requires that the test be repeated. If a positive result occurs from the repeat testing, the serum is titered and a confirmatory test is performed.
The VDRL test requires that the patient's serum sample be heat inactivated before the test. Charcoal is not a component of this test; cardiolipin-lecithin-cholesterol antigen is used and the serum/antigen mixture is then examined with a microscope for evidence of clumping. The VDRL test can also be used with a cerebrospinal fluid sample rather than a blood sample.
If a chancre is present during the examination, a sample of fluid can be taken from the ulcer and examined with a specialized darkfield microscope to detect corkscrew-shaped T. pallidum. While this method of early diagnosis is extremely accurate, many patients do not have a chancre when they seek treatment or are in a later stage of infection. Treponemals are the first antibodies to appear in a syphilis patient and remain elevated for life. Nontreponemal antibodies appear in 1–4 weeks after infection and remain elevated until treatment begins or the patient moves into a later stage of infection.
Because these antibodies are present at different stages of the disease, the validity of the specific test depends on when it is used relative to the patient's stage of disease. The approximate percentages of how sensitive the tests are in detecting syphilis relative to the patient's stage of disease are as follows:
- VDRL: 70% primary stage; 100% secondary stage; 95% latent stage; 71% late stage.
- RPR: 86% primary stage; 100% secondary stage; 98% latent stage; 73% late stage.
- FTA-ABS: 84% primary stage; 100% secondary stage; 100% latent stage; 96% late stage.
- MHA-TP: 76% primary stage; 100% secondary stage; 97% latent stage; 94% late stage.
Insurance coverage varies greatly between plans, and these tests may or may not be covered by the insurance provider. Patients should check with their insurance provider for specifics as to cost and coverage of these tests.
The patient should receive basic information about syphilis, STDs, and the possible results of the test. Patients should not drink alcohol 24 hours before a VDRL test. The health care provider should obtain a complete medical history of the patient since other conditions can create false-positive test results.
The patient should be comforted and direct pressure should be applied to the venipuncture site for several minutes or until the bleeding has stopped. An adhesive bandage may be applied, if appropriate. If swelling or bruising occurs, ice can be applied to the site. Since many patients find needles unpleasant and are often fearful of the blood collection process, the health care provider should always reassure and monitor the patient for nervousness or fainting.
Careful vein and equipment selection are paramount to successful venipuncture. Veins that are too small can collapse and yield an insufficient sample. Probing with the needle can cause extensive bruising. Shaking the tube vigorously, collecting an insufficient sample, or using the wrong tube required for the sample are unacceptable and will require a second venipuncture. In normal circumstances, a blood draw for RPR or VDRL testing only takes a few minutes, while the patient experiences minor discomfort and a minute puncture wound at the site of the venipuncture.
The test results are reported as follows:
- RPR: negative or reactive.
- VDRL: Negative, weakly reactive, reactive.
- Titer: Reported as the highest dilution of serum that is reactive.
- FTA-ABS: Negative, borderline, or reactive.
Health care team roles
The non-physician health care provider is an important partner in laboratory testing. In accordance with the physician's orders, the nurse, blood collection specialist (phlebotomist), or laboratory professional usually prepares the patient, performs the blood draw, and readies the specimen for transport to either an internal or external laboratory for testing.
The health care provider that performs the venipuncture procedure should be trained in correct technique, vein selection, appropriate equipment selection, and infection control procedures. Health care providers must follow strict guidelines on processing and disposing of items containing blood or body fluids to control for contamination and infection.
The non-physician health care provider can be an important resource for patients with a STD. Often, these providers counsel patients, provide literature and pamphlets on STDs, provide information on using condoms during sexual intercourse, and can reassure the patient about treatment regimens. Patients with syphilis may be embarrassed about their condition or hesitant to seek medical attention. The effective health care provider supplies information in a supportive and non-judgmental environment that reassures the patient that he or she has made a positive step in obtaining medical care. The medical professional also informs the patient that he or she will require periodic retesting to evaluate the infection and monitor the effectiveness of treatment. Since syphilis is transmitted sexually, health care providers should work with the patient to obtain the names of sexual partners so that they may also be tested.
Fischbach, Frances. "Diagnosis of Sexually Transmitted Disease." In A Manual of Laboratory & Diagnostic Tests. 6th ed. Philadelphia: Lippincott Williams & Wilkins, 2000, pp. 538–543.
Hofmeister, Erik K., et al. "Spirochete Infections." In Clinical Diagnosis and Management by Laboratory Methods, edited by John Bernard Henry. 19th ed. Philadelphia: W. B. Saunders Company, 1996, pp.1183–1187.
Kee, Joyce LeFever. "VDRL." In Laboratory & Diagnostic Tests with Nursing Implications. 5th ed. Stamford, CT: Appleton & Lange, 1999, pp. 441–443.
Musher, Daniel M., and Robert E. Baughn. "Syphilis." In Infectious Diseases, edited by Sherwood L. Gorbach, John G. Bartlett, and Neil R. Blacklow. 2nd ed. Philadelphia: W. B. Saunders Company, 1997, pp. 980–986.
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Antibody —A specific protein created by the immune system in response to an invading infectious organism.
Antigen —A protein covering a foreign invader in the body (like a bacterium); the immune system produces antibodies to combat antigens and fight disease.
Darkfield microscope —A specialized microscope with a unique condensor that manipulates the light. Objects seen through this microscope appear white against a dark background.
Direct florescence —A laboratory process using the application of dyes that can glow in specific conditions when applied to a specimen and can be seen with an ultraviolet microscope.
Edematous —The state of having swelling (edema) caused by the collection of excess fluid within tissues.
Hematoma —Swelling and subsequent bruising when blood leaks from a vein into local tissues; can be caused by improper venipuncture when the needle has gone through a vein or when the needle has been inserted incorrectly.
Titer —A central concept in serologic testing; determines the concentration of an antibody (if present) in a blood sample. A high titer indicates that a considerable amount of an antibody is present in a blood sample.
Venipuncture —Puncture of a vein with a needle for the purpose of withdrawing a blood sample for analysis.
American Social Health Association. P.O. Box 13827, Research Triangle Park, NC 27709. (919) 361-8400. <http://www.ashastd.org>.
"Sexually Transmitted Disease." Fast Stats A to Z of the National Center for Health Statistics. <http://www.cdc.gov>, compiled from 1998.
Linda D. Jones, B.A., PBT (ASCP)