Syphilis serology interpretation (RPR/TPHA titres, treatment response)
Core concept
| Non-treponemal (RPR, VDRL) | Treponemal (TPPA/TPHA, EIA/CMIA, FTA-ABS) | |
|---|---|---|
| Antigen | Cardiolipin - a host lipid, not treponemal | T. pallidum antigens |
| Reported as | A titre (1:1, 1:2, 1:4 ...) | Reactive / non-reactive |
| Role | Disease ACTIVITY and response to treatment | Confirms exposure |
| After successful treatment | Falls - a 4-fold (2-dilution) drop = cure | Stays reactive for LIFE in ~85% |
- One test tells you whether they have ever had it; the other tells you whether it is active now. You need both.
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