Why Nontreponemal?

There are two different types of serologic assays for syphilis; nontreponemal and treponemal. A nontreponemal assay (traditional algorithm), such as the rapid plasma reagin (RPR) test, is an indicator of an active or recent syphilis infection and can be used to monitor response to therapy over time. The nontreponemal testing algorithm is recommended by the CDC, preferred by doctors and used in a majority of labs for syphilis screening.

A treponemal test (reverse algorithm) cannot differentiate between active or previously treated infection, which can create a false-positive result. The immune response to syphilis creates antibodies to fight the infection; those antibodies remain in the blood after successful treatment, because treponemal tests cannot monitor the response to therapy.

Trep vs Nontreponemal syphilis testing.
  • A  2015 study by the CDC determined that nontreponemal tests can detect infection up to 14 days earlier than treponemal tests.
  • CDC recommended algorithm
  • Preserve valuable blood resources
  • Reduce confusion among clinicians
Serologic study of syphilis

CDC Recommended Algorithm

“The CDC continues to recommend the traditional screening algorithm using a nontreponemal test (e.g., RPR or VDRL), with reactive nontreponemal tests confirmed by treponemal testing.”

Gail Bolan, MD; Director, Division of STD Prevention; National Center For HIV/AIDs, Viral Hepatitis, STD, and TB Prevention

A graphic showing the CDC recommended traditional algorithm versus the reverse sequence method.

Advantages of Traditional Nontreponemal RPR Testing

  • CDC recommended
  • Detect, diagnose and monitor
  • Most cost effective algorithm
  • Fewer false reactives
  • Lower total healthcare cost
  • Less patient follow-ups
  • Less overtreatment
  • Standardized methodology
  • Results providers trust/know
  • Low cost/test