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Introduction ⬇

Syphilis is a sexually transmitted infection (STI) caused by Treponema pallidum, a spirochete with closely wound coils approximately 8–15 μm long. Untreated, the disease progresses through three stages that can extend over many years and become life-threatening.

Antibodies to syphilis begin to appear in the blood 4–6 weeks after infection (Table 8.2). Nontreponemal tests determine the presence of reagin, which is a nontreponemal autoantibody directed against cardiolipin antigens. These tests include the rapid plasma reagin (RPR) and Venereal Disease Research Laboratory (VDRL) tests. The U.S. Centers for Disease Control and Prevention (CDC) recommends these tests for syphilis screening; however, they may show negative results in some cases of late syphilis. Biologic false-positive results can also occur (Table 8.3).

Conversely, treponemal (i.e., specific) tests detect antibodies to T. pallidum. These tests include the passive particle agglutination T. pallidum test (TP-PA) and the fluorescent treponemal antibody absorption test (FTA-ABS). These tests confirm syphilis when a positive nontreponemal test result is obtained. Because these tests are more complex, they are not used for screening. Certain states require automatic confirmation for all reactive screening tests by using a treponemal test such as the TP-PA or FTA-ABS.

A positive reaction is not conclusive for syphilis. Several conditions produce biologic false-positive results for syphilis. Biologic false-positive reactions are by no means “false.” They may reveal the presence of other serious diseases. It is theorized that reagin (reaction) is an antibody against tissue lipids. Lipids are presumed to be liberated from body tissue in the normal course of activity. These liberated lipids may then induce antibody formation. Nontreponemal biologic false-positive reactions can occur in the presence of drug abuse, lupus erythematosus, mononucleosis, malaria, leprosy, viral pneumonia, recent immunization, or, on rare occasions, pregnancy. False-negative reactions may occur early in the disease course or during inactive or later stages of disease.

Normal Findings ⬆ ⬇

Sensitivity of FTA-ABS

  • Primary syphilis: 84%

  • Secondary syphilis: 100%

  • Latent syphilis: 100%

  • Late syphilis: 96%

Sensitivity of TP-PA

  • Primary syphilis: 86%

  • Secondary syphilis: 100%

  • Latent syphilis: 100%

Procedure ⬆ ⬇

  1. Collect a 7-mL blood serum sample in a red-topped tube. Observe standard precautions. Fasting is usually not required.

  2. Label the specimen with the patient’s name, date, and tests ordered and place in a biohazard bag for transport to the laboratory.

Procedural Alert

If the RPR test is used, the following need to be observed:

  1. Excess chyle released into the blood during digestion interferes with test results; therefore, the patient should fast for 8 hours.

  2. Alcohol decreases reaction intensity in tests that detect reagin; therefore, alcohol ingestion should be avoided for at least 24 hours before blood is drawn.

Clinical Implications ⬆ ⬇

  1. Diagnosis of syphilis requires correlation of patient history, physical findings, and results of syphilis antibody tests. T. pallidum is diagnosed when both the screening and the confirmatory tests are reactive.

  2. Treatment of syphilis may alter both the clinical course and the serologic pattern of the disease. Treatment related to tests that measure reagin (RPR and VDRL) includes the following measures:

    1. If the patient is treated at the seronegative primary stage (e.g., after the appearance of the syphilitic chancre but before the appearance of reaction or reagin), the VDRL remains nonreactive.

    2. If the patient is treated in the seropositive primary stage (e.g., after the appearance of a reaction), the VDRL usually becomes nonreactive within 6 months of treatment.

    3. If the patient is treated during the secondary stage, the VDRL usually becomes nonreactive within 12–18 months.

    4. If the patient is treated more than 10 years after the disease onset, the VDRL usually remains unchanged.

  3. A negative serologic test may indicate one of the following circumstances:

    1. The patient does not have syphilis.

    2. The infection is too recent for antibodies to be produced. Repeat tests should be performed at 1-week, 1-month, and 3-month intervals to establish the presence or absence of disease.

    3. The syphilis is in a latent or inactive phase.

    4. The patient has a faulty immunodefense mechanism.

    5. Laboratory techniques were faulty.

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain test purpose and procedure. Assess for interfering factors. Instruct the patient to abstain from alcohol for at least 24 hours before the blood sample is drawn.

  2. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient regarding abnormal findings. Explain biologic false-positive or false-negative reactions. Explain the need for possible follow-up testing.

  2. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Clinical Alert

  1. Sexual partners of patients with syphilis should be notified and evaluated for the disease.

  2. After treatment, patients with early-stage syphilis should be tested at 3-month intervals for 1 year to monitor for declining reactivity.

Interfering Factors ⬆

  1. Hemolysis can cause false-positive results.

  2. Hepatitis can result in a false-positive test.

  3. Testing too soon after exposure can result in a false-negative test.