Syphilis Screening: Qualitative vs Quantitative RPR
For initial syphilis screening in sexually active adults with new or multiple partners, you should always order a quantitative RPR test, not a qualitative one. 1, 2
Why Quantitative Testing is Essential
Quantitative titers are critical for establishing a baseline that enables proper monitoring of disease activity and treatment response. 1, 2 The Centers for Disease Control and Prevention explicitly recommends always requesting quantitative titers (e.g., 1:4,1:16,1:64) rather than just "positive/negative" results. 1
Key Clinical Reasons:
Baseline documentation: A quantitative titer at diagnosis provides the reference point needed to assess treatment success, which is defined as a fourfold decline in titer within 6-12 months. 1, 2
Distinguishing active from past infection: When combined with treponemal testing, the quantitative RPR titer helps differentiate new infection from previously treated syphilis or serofast state (persistent low titers after adequate treatment). 1
Detecting treatment failure or reinfection: A sustained fourfold increase in titer compared to baseline indicates either treatment failure or reinfection, but this determination is impossible without an initial quantitative value. 1, 2
Risk stratification: Higher titers (≥1:8) are highly specific for true infection, with false-positive results being extremely rare at this threshold. 1
Practical Implementation
Order "quantitative RPR" explicitly on the laboratory requisition to ensure the lab reports titers to endpoint dilution, not just a qualitative positive/negative result. 1
Use the same testing method consistently (RPR vs VDRL) for all follow-up testing, preferably by the same laboratory, as titers are not interchangeable between methods. 1, 2
For high-risk populations (men who have sex with men, multiple partners, sex workers, HIV-infected individuals), screening should occur every 3-6 months, and quantitative titers at each screening enable detection of new infections against a known baseline. 3, 1
Common Pitfall to Avoid
Never accept a qualitative RPR result for initial screening. If your laboratory reports only "reactive" or "nonreactive" without a titer, contact them immediately to request quantitative testing on the same specimen. 1 Without this baseline titer, you will be unable to properly monitor treatment response or distinguish reinfection from treatment failure in the future. 1, 2