Syphilis Diagnosis Guidelines

Diagnostic Testing Algorithm

The Centers for Disease Control and Prevention recommends performing both nontreponemal and treponemal tests for complete diagnosis of syphilis, as using only one type of test is insufficient for accurate diagnosis 1
Darkfield examinations and direct fluorescent antibody tests of lesion exudate or tissue are the definitive methods for diagnosing early syphilis, and should be prioritized when lesions are present 1, 2, 3

Nontreponemal tests, such as VDRL or RPR, correlate with disease activity and should be reported quantitatively, with a fourfold change in titer indicating a clinically significant difference 1
Treponemal tests, such as FTA-ABS or TP-PA, remain reactive for life in most patients regardless of treatment or disease activity, but may revert to nonreactive in 15-25% of patients treated during the primary stage 1, 2

Sequential serologic tests should use the same testing method, preferably by the same laboratory, to monitor treatment response 1
A fourfold change in titer, or two dilutions, indicates a clinically significant difference in treatment response 1

In HIV-infected patients, standard serologic tests remain accurate and reliable, but some patients may have atypical serologic test results, and additional testing may be necessary 1
For neurosyphilis diagnosis, no single test is sufficient, and diagnosis typically requires a combination of reactive serologic test results, abnormal CSF cell count or protein, and reactive VDRL-CSF 1, 3

Using only one type of test can lead to misdiagnosis, and failure to report nontreponemal test results quantitatively limits the ability to monitor treatment response 1
Comparing titers between different test types, such as VDRL and RPR, can lead to incorrect conclusions, and relying on treponemal tests to assess treatment response is inappropriate 1, 2

The Centers for Disease Control and Prevention recommends that patients with a reactive treponemal test (TP-A/FTA-ABS) and non-reactive nontreponemal test (RPR) should receive treatment for late latent syphilis with benzathine penicillin G 2.4 million units IM weekly for 3 weeks, as this serologic pattern can represent late latent syphilis or tertiary syphilis with waning nontreponemal antibodies 4, 5
The serologic pattern TP-A+/RPR- can also represent false-positive treponemal test, although less likely with FTA-ABS 6, 5

The sensitivity of nontreponemal tests varies by stage of infection, with a sensitivity of 70-80% in primary syphilis, 97-100% in secondary syphilis, 61-76% in late latent syphilis, and 47-64% in tertiary syphilis 4, 5
A non-reactive RPR with reactive TP-A is commonly seen in late syphilis, where nontreponemal antibodies have declined over time 4, 5

The Centers for Disease Control and Prevention recommends administering benzathine penicillin G 2.4 million units IM once weekly for 3 weeks (total 7.2 million units) for patients with no documented adequate treatment history 7

Some HIV-infected patients may have atypical serologic patterns, but standard serologic tests remain accurate for most HIV patients 7
VDRL-CSF is highly specific but insensitive for neurosyphilis, and CSF leukocyte count >5 WBCs/mm³ is a sensitive indicator for neurosyphilis 7

No follow-up serologic testing is needed if treating presumed late latent syphilis with documented prior adequate treatment, but for newly diagnosed and treated late latent syphilis, clinical follow-up is recommended, although serologic response may be minimal 7