Presumptive dx1 requires 2 tests 2 nontreponemal VDRL or RPR 3 treponemal FTA ABS TP PA various EIAs others 4

¹ Darkfield exam and tests to detect <i>T pallidum</i> directly from lesion exudate/tissue are the definitive methods for early syphilis dx. Although no <i>T pallidum</i> detection tests are commercially available, some labs provide locally developed/validated PCR tests.<br><br>
² Use of only 1 type of test insufficient for dx and can result in false-negative results in 1° syphilis and false-positive results in pts w/o syphilis. False-positive nontreponemal test results can be assoc w/ other infxns (eg, HIV), autoimmune dz, immunizations, pregnancy, IDU, and older age. Therefore, pts w/ a reactive nontreponemal test should always have treponemal test to confirm dx.
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³ VDRL and RPR are equally valid assays, but quantitative results from the 2 tests cannot be compared directly because RPR titers frequently are slightly higher than VDRL titers.
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⁴ Although many treponemal-based tests are commercially available, only a few are approved for use in the U.S.
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⁵ A 4-fold change in titer (eg, 1:16→1:4 or 1:8→1:32), is considered necessary to demonstrate a clinically significant difference between 2 nontreponemal test results obtained using the same serologic test. Sequential serologic tests in individual pts should be performed using the same testing method (VDRL or RPR), preferably by the same lab. Nontreponemal test titers usually decline after tx and might become nonreactive w/ time; however, in some persons, nontreponemal antibodies can persist for a long period of time (“serofast rxn”).
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⁶ However, 15%–25% of pts treated during the primary stage revert to being serologically nonreactive after 2–3y.
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⁷ Atypical nontreponemal serologic test results (ie, unusually high, unusually low, or fluctuating titers) might occur regardless of HIV-infxn status.
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⁸ Examples of neurosyphilis signs: cranial nerve dysfunction, auditory/ophthalmic abnormalities, meningitis, stroke, acute or chronic altered mental status, and loss of vibration sense.
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⁹ In pts w/ HIV infxn, CSF leukocyte count usually is elevated (>5 WBC/mm³). Using a higher cutoff (>20 WBC/mm³) might improve specificity of neurosyphilis dx.
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¹⁰ No single test can be used to diagnose neurosyphilis in all instances. Dx depends on combo of CSF tests in presence of reactive serologic tests and neuro s/sx. CSF-VDRL is highly specific but insensitive. In a pt w/ neuro s/sx, a reactive CSF-VDRL (in absence of blood contamination) is considered diagnostic of neurosyphilis. When CSF-VDRL is negative despite presence of clinical signs of neurosyphilis, reactive serologic test results, and abnormal CSF cell count and/or protein, neurosyphilis should be considered. In this instance, additional eval using FTA-ABS testing on CSF may be warranted. CSF FTA-ABS test is less specific for neurosyphilis than CSF-VDRL but is highly sensitive. Neurosyphilis highly unlikely w/ a negative CSF FTA-ABS, esp among pts w/ nonspecific neuro s/sx.