A positive EIA treponema-specific test (e.g. Trep-Sure) suggests either current or prior syphilis. It should be followed by an RPR to better assess disease activity (1). If the RPR is positive, syphilis can be assumed and further evaluation for neurosyphilis with lumbar puncture may be necessary in this elderly patient with neurological symptoms.
If the RPR is negative, a more specific treponema test (e.g. fluorescent tryponemal antibody [FTA], or Treponema pallidum particle agglutination [TP-PA]) should be performed for confirmation of the treponema-specific test (1).
Recall that the treponema-specific antibody tests by EIA are much more sensitive and specific than RPR, especially during the primary and late stages of syphilis. Also remember that serum RPR may be negative in about 30% of patients with neurosyphilis (2); so a negative serum RPR should not rule out neurosyphilis.
1. Binnicker MJ, Jespersen DJ, Rollins LO. Treponema-specific tests for serodiagnosis of syphilis: comparative evaluation of seven assays 2011;49:1313-1317. https://www.ncbi.nlm.nih.gov/pubmed/21346050
2. Whitefield SG, Everett As, Rein MF. Case 32-1991;tests for neurosyphilis. N Engl J Med 1992;326:1434. https://www.ncbi.nlm.nih.gov/pubmed/1569992