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Laboratory

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RPR/VDRL/MHA-TP (Serologic Tests for Syphilis)
Darkfield/FTA-ABS Microscopy

A variety of serologic tests for syphilis are available, including:
  • VDRL (Venereal Disease Research Laboratory)
  • RPR (Rapid Plasma Reagin)
  • FTA-ABS (Fluorescent Treponemal Antibody Absorption)
  • TP-MHA (Treponema Pallidum Microhemagglutination Assay)

Each differs the others in the precise substance being measured, complexity, and specificity. All are satisfactory for use in managing syphilis. Abnormals may be:

  • Reactive,
  • Weakly reactive, or
  • Bordeline

Whenever a screening test (RPR, VDRL) is positive, a more specific test (FTA-ABS, TP-MHA) should be used to confirm the test and rule out a "biologic false positive."

A negative or "nonreactive" test may indicate:

  • The patient doesn't have syphilis
  • The patient has syphilis, but is so early in the course of the disease that the test has not yet turned positive. In these cases, the test may never turn positive if the patient is effectively treated.
  • The patient had primary syphilis, had a positive test, was effectively treated, 6 months have passed and the test has now reverted back to negative.
  • The patient had secondary syphilis, had a positive test, was effectively treated, 12-18 months have passed and the test has now reverted back to negative.
  • The patient has syphilis, but his/her immune system is impaired.

A positive or "reactive" test may indicate:

  • The patient has syphilis.
  • The patient had syphilis, was effectively treated, but the test has not yet returned to negative:
    • With primarily syphilis, it typically takes about 6 months for the test to turn negative.
    • With secondary syphilis, it typically takes 12-18 months for the test to turn negative.
    • The longer syphilis remains untreated, the longer it will take for the test to return to normal, and the less likely it is to ever return to normal.
  • The patient has a biologic false positive (BFP)

Normal Values*

Serologic Test for Syphilis Negative

*These are general values taken from a variety of sources. The actual normal values may vary from lab to lab and from one type of testing protocol to another.



Spirochetes



Darkfield View of Spirochetes



Positive FTA-ABS

Source: Operational Medicine 2001,  Health Care in Military Settings, NAVMED P-5139, May 1, 2001, Bureau of Medicine and Surgery, Department of the Navy, 2300 E Street NW, Washington, D.C., 20372-5300

Military Obstetrics & Gynecology
2003, 2004, 2005, 2006 Medical Education Division, Brookside Associates, Ltd.
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