Retrospective comparison between non-treponemal and treponemal tests for screening of blood donors for syphilis and their correlation with donor history in a tertiary care teaching hospital.

BACKGROUND AND OBJECTIVES

Treponemal tests provide advantage of better detection during early, late and latent stages of syphilis with equal or higher sensitivity & specificity in comparison to non-treponemal tests. The objective of the present study was to analyse the level of concordance between treponemal and non-treponemal tests for donor screening and to correlate them with donor history.

MATERIALS AND METHODS

Retrospective analysis of syphilis screening by treponemal (Chemiluminescence & TPHA) and non-treponemal tests (RPR) was done and donor history for high-risk behaviour and factors associated with false positivity were collected from post-donation counselling and collected data was coded and analysed.

RESULTS

Amongst the 12,000 donors screened, reactivity rate by RPR, TPHA and Chemiluminescence was 0.45%, 0.8% and 1.17% respectively. There was discordance of 62% and 32% for reactive results by RPR and TPHA respectively when compared with Chemiluminescence. History of high-risk behaviour was present in ∼ 50% and 15% of donors with discordant results by RPR and TPHA respectively. Of 34 donors who were reactive only by Chemiluminescence and were followed up, 15% had history of high-risk behaviour and 56% had factors associated with false reactivity.

CONCLUSION

Treponemal tests showed high syphilis reactivity amongst blood donors as compared to non-treponemal tests most likely due to their ability to detect early, late and latent syphilis cases. This may confer added transfusion safety in centres dependent on replacement donors without NAT testing by identifying donors with high-risk history with negligible increase in discard rate due to false reactivity.