A 25-year-old man presents with a painless indurated penile ulcer of 4 days duration. Dark-field microscopy is negative. VDRL is non-reactive. Which statement about the optimal timing and interpretation of serologic testing in early primary syphilis is correct?
- A VDRL becomes reactive approximately 3 weeks after the chancre appears, so testing should be repeated at that point
- B FTA-ABS becomes reactive approximately 1 week before VDRL, so it should be tested now for earlier diagnosis ✓
- C TPHA is the first serologic test to become reactive and should be ordered as the definitive test today
- D A non-reactive VDRL at 4 days after ulcer onset rules out syphilis, and no further testing is needed
Correct answer: B. FTA-ABS becomes reactive approximately 1 week before VDRL, so it should be tested now for earlier diagnosis
Explanation
In primary syphilis, treponemal-specific tests (FTA-ABS, TP-EIA) become reactive about 1 week earlier than non-treponemal tests (VDRL/RPR). The VDRL is reactive in only about 75 percent of primary syphilis cases, becoming positive roughly 1 to 2 weeks after the chancre appears. Therefore, a negative VDRL at day 4 does not exclude syphilis, and a treponemal test should be performed for earlier detection. TPHA is not the earliest reactive test.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.