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Skills: Screening tests for syphilis
When you have completed this skills chapter you should be able to:
- Screen a patient for syphilis with the syphilis rapid test and the RPR card test.
- Interpret the results of the screening tests.
At the first antenatal visit each woman should be screened for syphilis. This could be done at the clinic with the syphilis rapid test (Determine Syphilis TP) or RPR card test. If syphilis is diagnosed, the patient must be informed and treatment must be started immediately at the antenatal clinic. Positive rapid screening tests must be confirmed with a laboratory RPR or VDRL test. The syphilis rapid test or RPR card test can be used in any antenatal clinic, as no sophisticated equipment is required.
Syphilis rapid test
The syphilis rapid test is a specific test for syphilis and will become positive when there are antibodies against Treponema pallidum (the organism that causes syphilis) in the blood. The test result corresponds to that of a TPHA or FTA test which are also specific tests for syphilis.
A. Equipment needed to perform a syphilis rapid test
- The Abbott Determine TB Whole Blood Essay. Each kit contains 10 cards with 10 tests. The Chase Buffer (2.5 ml bottle) is supplied with the kit.
- EDTA capillary tubes marked to indicate 50 μl, lancets, alcohol swabs and sterile gauze swabs. These are not supplied with the kit.
The kit needs to be stored at room temperature between 2 °C and 30 °C. Storage in a fridge is required during summer time. The kit must not be used after the expiry date.
B. Performing the syphilis rapid test
- Clean the patient’s fingertip with an alcohol swab and allow the finger to dry.
- Remove a test strip from the foil cover.
- Prick the skin of the fingertip with a lancet. Wipe the first drop of blood away with a sterile gauze swab.
- Collect the next drop of blood into the EDTA tube. Either side of the tube can be used to collect blood. Fill the tube from the tip to the first black circle (i.e. 50 μl blood). Avoid the collection of air bubbles.
- Apply the 50 μl of blood from the EDTA tube onto the sample pad marked with an arrow on the test strip.
- Wait until all the blood has been absorbed into the sample pad and then apply 1 drop of Chase Buffer. The bottle must be held vertically (upside down) above the test strip when a drop of the buffer is dropped onto the sample pad.
- Wait a minimum of 15 minutes and then read the result. The maximum waiting time for reading the test is 24 hours. After 24 hours the test becomes invalid.
C. Reading the results of the syphilis rapid test
- Positive: A red bar will appear within both the Control window and the Patient window on the test strip. Any visible red bar in the Patient window must be regarded as positive.
- Negative: A red bar will appear within the Control window but no red bar is seen in the Patient window.
- Invalid: If no red bar appears in the Control window, even if a red bar is visible in the Patient window, the result is invalid and the test must be repeated.
D. The interpretation of the syphilis rapid test
- A positive test indicates that a person has antibodies against syphilis. This means that the person either has active (untreated) syphilis or was infected in the past and no longer has the disease.
- A negative test indicates that a person does not have antibodies and cannot have syphilis, either in the present or past, unless the person was infected very recently and has not yet formed antibodies.
E. Management if the syphilis rapid test is positive
- Explain to the patient that the screening test for syphilis is positive but that this should be confirmed or rejected by a laboratory test (RPR or VDRL test).
- It is advisable, however, that treatment with penicillin be started immediately so that the fetus can be treated while waiting for the result of the laboratory test.
- Ask the patient to return in 1 week for the result of the laboratory test.
F. Interpretation of the RPR or VDRL test when the syphilis rapid test is positive
- If the RPR or VDRL is negative the patient does not have syphilis. Treatment can be stopped.
- If the RPR or VDRL titre is 1:16 or higher the patient has syphilis and must be treated with a full course of 3 doses of benzathine penicillin (Bicillin LA of Penilente LA).
- If the RPR of VDRL titre is 1:8 or lower and the patient and her partner have been fully treated in the past 3 months, treatment can be stopped. Otherwise, a full course of 3 doses of benzathine penicillin must be given.