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MS WordPerinatologist Corner - C.E.U/C.M.E. Modules
Syphilis in Pregnancy
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6. Approach to Testing for Syphilis in Pregnancy
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Areas where the prevalence of congenital syphilis has become a problem have repeated testing again at 28 weeks and/or at delivery. Any woman who presents with a fetal demise should have her serology repeated as part of the stillbirth workup. Any woman found to have fetal hydrops on ultrasound should have her serology repeated also. It is prudent to offer testing for HIV to women with a positive syphilis serology as well. Remember that women with a positive non-treponemal test should have it confirmed with a treponemal test to be sure it is not a false positive. If not reflexively provided for you, a titer should also be requested.
What to do with a positive test?
A positive test should also prompt investigation of the patient's history. Has she been treated for syphilis in the past? Most patients will be aware of the diagnosis and remember the treatment. While contact of sexual partners and case finding is the norm with public health departments, you should of course approach this discretely and in a non-judgmental fashion with your patient first. Was her partner treated? Is this a new partner? The history is also important to try to decide in what stage the patient may be, and what the appropriate treatment should be. In conjunction with the history, the titer will also help you decide on the stage, and on the treatment indicated. Low titers may indicate new, or recurrent, primary syphilis, or they may represent latent, untreated disease, or, most commonly, and as indicated by the history, they may represent old, previously treated disease. Very high titers (>1:32) usually indicate recent onset, active, disease, especially second stage syphilis. A physical exam looking for a chancre (primary syphilis), or the rash, patchy alopecia, and/or condylomata lata (secondary syphilis), is always appropriate.
What about false positives?
A false positive serology is diagnosed when the non-treponemal test (VDRL or RPR) is positive but the treponemal test (FTA or TP-PA) is negative. Since the FTA will be positive even before the VDRL or RPR becomes reactive, this diagnosis can usually be made immediately. False positive treponemal tests are uncommonly seen in the United States, but may be due to infection with other spirochetal infections, such as Lyme disease, leprosy, relapsing fever, and leptospirosis. False positive non-treponemal tests may result from a long list of infectious and non-infectious causes. The non-infectious causes are nonspecific and include multiple prior pregnancies, intravenous heroin use, connective tissue disease (especially lupus), advanced malignancy, and multiple transfusion therapy, all conditions where other cross-reacting antibodies may be found. Many times a “biologic false positive” will just be a non-specific finding and may not represent disease at all. The infectious causes are far less common in our population, but can include concurrent pneumococcal or mycoplasma pneumonia, scarlet fever, bacterial endocarditis, tuberculosis, hepatitis, and infectious mononucleosis, among other more exotics. In the absence of an obvious history, a preliminary workup should include an anti-nuclear antibody (ANA) and a PPD. For confirmation and reassurance that this is indeed a false positive, the titer and FTA should be repeated in 2-3 weeks.
