Italian National Survey of Blood Donors: External Quality Assessment (EQA) of Syphilis Testing

The detection of syphilis among blood donors may reveal high-risk sexual behavior, which can go unreported at the time of donor selection and compromise the safety of the donated blood. In Italy, blood is collected, tested, and distributed by transfusion services (TSs), which also perform outpatient transfusions. Although the TSs must screen for syphilis by law, there are no indications of the specific type of method to be used, generating discrepancies in the results obtained by the different TSs. To determine the proficiency of the TSs in screening for syphilis, we performed an external quality assessment (EQA). The EQA was based on two shipments of serum panels; 133 and 118 of the 326 existing TSs participated in the first and second shipments, respectively. Each panel consisted of both positive and negative serum samples. The results confirmed that the use of a single nontreponemal test (the Venereal Disease Research Laboratory [VDRL] and the rapid plasma reagin [RPR] tests) is the least sensitive means of identifying samples that are positive for syphilis antibodies. We also found that the interpretation of the results of manual techniques, such as the RPR test, the VDRL test, the Treponema pallidum hemagglutination (TPHA) assay, and the T. pallidum particle agglutination (TPPA) assay, can vary greatly among different TSs and operators. Total Ig enzyme immunoassays (EIAs) are the most sensitive. However, the determination of syphilis on the basis of the results of a single test is not sufficient for an accurate screening; and all blood units should thus be assessed by two distinct treponemal tests, that is, a total Ig EIA and the TPHA or the TPPA assay.Syphilis is a reemerging disease and is caused by the spirochete Treponema pallidum. In most cases it is sexually transmitted, although it can also be transmitted from mother to child in utero and, rarely, through blood transfusion, especially through the transfusion of fresh blood components (6, 12). Serological tests for syphilis are considered to be a milestone in syphilis control, and since as early as the 1930s they have greatly contributed to the detection of T. pallidum infection not only in the clinical setting but also in transfusional medicine. The detection of blood donors who are positive for syphilis is an important public health concern, given that testing may reveal high-risk sexual behavior, which can go unreported at the time of donor selection and compromise the safety of blood used for transfusions.In some European countries, the occurrence of T. pallidum infection in the general population has been increasing, and this increase is reflected in its growing occurrence among blood donors. In particular, a survey performed in England has indicated that since 2001 there has been a trend toward a moderate increase in the incidence of T. pallidum infection among blood donors (2). In Germany, although the incidence of infection among donors is very low, increases have been recorded since 1991 (9). The incidence of T. pallidum infection among blood donors is also increasing in Italy. In particular, according to the Transfusion Transmitted Infections Surveillance System (7), it increased from 3.8 per 100,000 donations in 1999 to 7 per 100,000 donations in 2006 (11).The data collected by the Transfusion Transmitted Infections Surveillance System in Italy are provided by the existing 326 transfusion services (TSs). These are hospital-based facilities where blood is collected, tested, and distributed and where, in most cases, outpatient transfusions are performed (10). In 2006, there were 1,539,454 donors, for a total of 2,402,267 donated units. Remarkably, 85% of the donors provided multiple donations (4). Although the TSs are required by law to screen for syphilis, there are no indications of the specific type of method that must be used, nor is there any confirmatory algorithm for testing on the basis of the different assays available. In fact, the laboratory assessment of syphilis is generally based on the detection of antibodies against T. pallidum antigens in blood by the use of either specific or nonspecific reagents. Methods based on the detection of specific Treponema antigens include passive agglutination, such as the T. pallidum hemagglutination (TPHA) assay or the T. pallidum particle agglutination (TPPA) assay, and indirect immunofluorescence, such as the fluorescent treponemal antibody absorbed (FTA-ABS) assay or the most sensitive assay, the enzyme immunoassay (EIA), for the detection of specific IgG and IgM or total Ig. Additional methods are based on nonspecific reagents, including nontreponemal lipid antigens (cardiolipin), and they most commonly rely on the flocculation technique. Of these, the Venereal Disease Research Laboratory (VDRL) and rapid plasma reagin (RPR) tests are the most commonly used.The use of different assays from such a large array could generate discrepancies in the detection of syphilis among TSs, stressing the need for quality assessment. To this end, we performed an external quality assessment (EQA) of the quality and the comparability of the results obtained by the different TSs with the aim of contributing to the development of preventive and corrective measures (1, 3).