CONFIRMATORY SEROLOGICAL TESTING OF BLOOD-DONORS POSITIVE ON TPHA SCREENING IN SINGAPORE

Seventy-two blood donors who were tested positive by the Singapore Blo od Transfusion Service (SBTS) for Treponema pallidum haemagglutination (TPHA) test, were evaluated at the Department of Sexually Transmitted Diseases Clinic (DSC) between November 1994 to December 1996. All und erwent syphilis serological testing, including rapid plasma reagin tes t (RPR), TPHA test and fluorescent treponemal antibody-absorption (FTA -Abs) test. All except one (98.6%) were confirmed TPHA positive by the DSC. Of the 71 TPHA-confirmed-positive donors, 53 (74.6%) were subseq uently tested positive for FTA-Abs and 18 (25.4%) were tested negative for FTA-Abs. Twenty-two (31%) of the 71 TPHA-positive blood donors ha d reactive RPR and 49 (69%) had non-reactive RPR. Of the 22 TPHA-posit ive donors who had reactive RPR, 19 (86%) had positive FTA-Abs (13 lat e latent syphilis, 4 serological scar, one late congenital syphilis, o ne secondary syphilis), and 3 (14%) had negative FTA-Abs (all late lat ent syphilis). Of the 49 TPHA-positive donors who had non-reactive RPR , 34 (69%) had positive FTA-Abs (24 late latent syphilis, 9 serologica l scar, one late congenital, syphilis) and 15 (31%) had negative FTA-A bs (12 late latent syphilis, 2 serological scar, one false-positive TP HA). Only one TPHA-positive donor referred by the SETS subsequently tu rned out to have negative syphilis serology at the DSC. Overall, 68 (9 5.8%) TPHA-positive donors who had a past history of sexual exposure w ere managed as treated or untreated syphilis, regardless of their RPR or FTA-Abs results. However, FTA-Abs was found to be useful in the man agement of 3 (4.2%) TPHA-positive blood donors in the absence of a his tory of sexual Exposures.