Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1428 page)

   
Normal range:
Negative.

   Use

   An aid in the diagnosis of active or past
T
.
pallidum
infection. Nontreponemal tests are based upon the reactivity of serum from patients with syphilis to a cardiolipin–cholesterol–lecithin antigen. These tests measure IgG and IgM antibodies and are used as the screening test for syphilis in most settings. Positive tests are usually reported as a titer of antibody, and they can be used to follow the response to treatment in many patients. Treponemal tests are more complex and are usually used as confirmatory tests when the nontreponemal tests are reactive. These tests all use
T
.
pallidum
antigens and are based upon the detection of antibodies directed against treponemal cellular components. These tests are qualitative and are reported as reactive or nonreactive.

   Interpretation

   Limitations

   A nonreactive result does not totally exclude a recent (within the last 2–3 weeks)
T
.
pallidum
infection. Therefore, results need to be interpreted with caution.

   Detection of treponemal antibodies may indicate recent, past, or successfully treated syphilis infections and, therefore, cannot be used to differentiate between active and cured cases.

   False-positive tests for syphilis can occur with both nontreponemal and treponemal tests. A false-positive test result may be identified by a reactive nontreponemal test followed by a nonreactive treponemal test. It is estimated that 1–2% of the US population has false-positive nontreponemal test results. False-positive tests are particularly common during pregnancy.

   The syphilis serology tests may be reactive with sera from patients with yaws (
T
.
pallidum
subspecies pertenue) or pinta (
Treponema carateum
).

   With nontreponemal tests, biologic false-positive reactions have been reported in diseases such as infectious mononucleosis, leprosy, malaria, SLE, vaccinia, narcotic addiction, autoimmune diseases, and viral pneumonia.

   Despite active syphilis serologic tests may be negative in severely immunecompromised patients.

   CDC recommends standard (traditional) testing algorithm where initial screening with a nontreponemal test such as the RPR; a reactive specimen is then confirmed as a true positive with a treponemal test such as the TP-PA test. When results are reactive to both treponemal and RPR tests, persons should be considered to have untreated syphilis unless this is ruled out by treatment history. Persons who were treated in the past are considered to have a new syphilis infection if quantitative testing on an RPR test (or another nontreponemal test) reveals a fourfold or greater increase in titer.