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11.9 Syphilis Tests
The syphilis tests identify Treponema pallidum antibodies in a blood sample. Treponema pallidumis the bacterium that causes syphilis. A positive venereal disease research laboratory (VDRL) test or rapid plasma reagin (RPR) test does not mean that the patient has syphilis. Other conditions can cause a positive test result. Fluorescent treponemal antibody absorption (FTA-ABS), Microhemagglutination assay (MHA-TP), and Treponema pallidum particle agglutination assay (TPPA) remain positive even after the patient is suc- cessfully treated for syphilis. VDRL and RPR tests are negative when treatment for syphilis is successful.
A negative result does not rule out syphilis, since detectable antibodies can take 4 weeks to develop
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following the initial infection. Many syphilis tests can use either a blood sample or a sample of spinal fluid. Consult the healthcare facility’s policy for reporting diagnosed cases of syphilis to the local health department. There are seven types of syphilis tests:
1. Venereal disease research laboratory (VDRL): This test identifies anti-cardiolipin antibodies that are produced by a patient who has syphilis. Diseases including syphilis cause the production of anti-cardiolipin antibodies. Therefore this test is used for screening but not diagnosing syphilis.
2. Rapid plasma reagin (RPR): This test is similar to VDRL, except antibodies can be detected without the aid of a microscope.
3. Enzyme immunoassay (ELIA): This test identifies Treponema pallidum antibodies and is used for screening for syphilis. Additional testing is necessary to diagnose syphilis.
4. Fluorescent treponemal antibody absorption (FTA-ABS): This test identifies Treponema pallidum antibodies after the fourth week after the initial infection and is used to confirm other positive test results.
5. Treponema pallidum particle agglutination assay (TPPA): This test is similar to the FTA-ABS except it is not used to test spinal fluid.
6. Darkfield microscopy: This test identifies the Treponema pallidum bacterium under a darkfield microscope and is used to diagnose the early stage of syphilis.
7. Microhemagglutination assay (MHA-TP): This test is similar to TPPA.
Why the Test Is Performed
The test assesses for syphilis infection and treatment for syphilis infection.
Before Administering the Test
Assess if the patient has:• Had a blood transfusion recently
• Has liver disease, yaws, lupus, or HIV
• Has taken antibiotics
How the Test Is Performed
A sample of blood is taken from the patient’s vein. The patient will experience a tight feeling when the tourni- quet is tightened, a pinch or nothing at all when the needle is inserted into the vein, and pressure when a gauze pad is pressed against the insertion site to stop bleeding. It can take up to 10 minutes for bleeding to stop if the patient is taking anticoagulants (aspirin, coumadin). A small bruise might appear at the insertion site, which could become swollen following this test. This is called phlebitis. Applying a warm compress several times a day will reduce the swelling.
Teach the Patient
Explain why the sample is taken, that the sex partner must also be tested, that the patient should refrain from sexual intercourse until the test shows that that patient and the sex partner are no longer infected, that a diag- noses of syphilis may have to be reported to the health department, and that a negative test may not rule out syphilis since detectable antibodies can take four weeks to develop following the initial infection.
Understanding the Test Results
The syphilis test results are available in 10 days.
• Normal test results (nonreactive/negative): No antibodies found. No Treponema pallidum bacterium seen under the microscope.
• Abnormal test results (reactive/positive): Antibody regain found. Treponema pallidum bacterium seen under the microscope.
• Inconclusive test results (equivocal): Unclear if antibody regain found. Unclear if Treponema pallidum bacterium is seen under the microscope.
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Solved Problems
Antibody Tests
11.1 What are antibodies?
Antibodies are proteins made by the immune system that bind to bacteria, viruses, and other microorganisms to destroy the microorganism.
11.2 How are antibodies created?
• Blood transfusions reaction: The transfused blood has different antigens on the surface of its red blood cells than the patient’s red blood cells, which causes the immune system to produce antibodies that attack the transfused red blood cells.
• Rhesus factor sensitization: The Rh antigen is in the fetus’s blood (Rh positive), but not in the pregnant woman’s blood (Rh negative).
• Autoimmune hemolytic anemia: The patient’s immune system creates antibodies against the patient’s red blood cells
11.3 What is the purpose of the direct Coombs test?
The purpose of the direct Coombs test is to identify antibodies attached to the patient’s red blood cells.
11.4 What is an Rh antibody titer?
An Rh antibody titer is the test performed in early pregnancy to determine the mother’s blood type and to determine if the mother is Rh negative.
11.5 What is the indirect Coombs test?
The indirect Coombs test identifies antibodies that have not but could attach to the patient’s red blood cells if the patient’s blood is mixed with the fetal blood.
11.6 Why are antibody tests performed?
To assess blood transfusion reaction or potential reaction, Rh factor sensitization, and autoimmune hemolytic anemia.
11.7 What should be assessed before administering the antibody test?
Assess if there is reason for the patient not to take the test, such as a history of blood transfusions, recently administering contrast material IV or dextran injections, the patient was pregnant in the previous three months, or has taken cephalosporins, tetracyclines, tuberculosis medication, sulfa medication, or insulin.
11.8 What does a positive result of an antibody test mean?
Positive test results mean that the patient’s blood contains antibodies for the patient’s red blood cells (direct Coombs test), the patient’s blood is incompatible with transfusion donor’s blood (indirect Coombs test)—the blood is not transfused, or the Rh negative mother is Rh sensitized (indirect Coombs test). The healthcare provider monitors the pregnancy closely to prevent problems with the fetus if the fetus is Rh positive.
11.9 What does a negative result of an Rh sensitized test mean?
The Rh negative mother is not Rh sensitized (indirect Coombs test). The mother is administered the Rh immune globulin vaccine (RhoGAM).
Blood Culture
11.10 What is a blood culture?
A blood culture identifies the microorganism that has invaded the patient.
11.11 Why is the sensitivity test ordered?
The sensitivity test identifies the medication that kills the microorganism.
11.12 Why is a blood culture ordered?
A blood culture assesses the existence of bacteria or fungi in blood, for endocarditis, medication that will kill the microorganism, the cause of unexplained fever, and the effect of treatment of a
microorganism infection.
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11.13 What should be assessed before administering the blood culture?
Assess if the patient has recently been administered antibiotics, since this can affect the test results.
11.14 How long might a blood culture for a fungus infection take before results are known?
Test results for a fungus infection can take up to 30 days.
11.15 What is an abnormal false positive of a blood culture?
Abnormal false-positive: Contaminated sample or improper processing results in bacteria or fungi found in the blood sample but not in the patient’s blood.
11.16 What is a false negative of a blood culture?
Improper processing or improper sampling results in bacteria or fungi not found in the blood sample, but the patient’s blood is infected.
11.17 How is blood cultured in a laboratory?
A blood culture identifies the bacteria or fungi by allowing the microorganism to grow in a controlled environment and then examining the microorganism under a microscope.
Mononucleosis Tests
11.18 What is a monospot test?The monospot test identifies heterophil antibodies that form between 2 weeks and 9 weeks after the patient becomes infected.
11.19 What is an EBV antibody test?
The EBV antibody test is ordered when the patient shows symptoms of mononucleosis and the monospot test is negative.
11.20 What causes mononucleosis?
The Epstein-Barr virus causes mononucleosis.
11.21 Why might a false-negative result occur in a mononucleosis test?
A false-negative result can occur if the test is administered within 2 weeks of the patient being infected.
11.22 What should be assessed before administering the mononucleosis test?
Assess if the patient has lymphoma, hepatitis, rubella, cytomegalovirus, or lupus.
11.23 What might be meant by a high monospot test?
High (positive) heterophil antibody levels greater than 0 may indicate mononucleosis, rheumatoid arthritis, leukemia, hepatitis, or lymphoma.
11.24 What might a high EBV Antibody Test result mean?
Mononucleosis.
11.25 What does the presence of the IgG antibody indicate?
The presence of the IgG antibody indicates that the patient was exposed to the Epstein-Barr virus in the past. Most adults have the IgG antibody.
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