A study of treponema pallidum haemagglutination positive blood donors in Singapore.

The Treponema Pallidum Haemagglutination (TPHA) test has been used for screening of syphilis among blood donors in Singapore since September 1992. Among the 79 500 donations that were screened between September 1992 and December 1993, 191 were tested positive (incidence rate of 0.24%). Seventy-two donors (37.7%) were evaluated at the Department of Sexually Transmitted Disease Control clinic. Seventy-nine percent of these donors had high risk sexual exposure and 33.3% had a history of sexually transmitted diseases. Eighty-three percent of the donors were diagnosed to have late latent syphilis, 9.7% were diagnosed to have a serological scar and the remaining had secondary syphilis, early latent syphilis and a false positive reaction. At least 65.3% of these donors would have been missed if the reagin test was used alone as the screening test. Thus, the TPHA test is a good marker for screening those who have high risk sexual behaviour and it is a more sensitive test than the reagin test for screening blood donors.