Syphilis and blood donors. Comparison of two different diagnostic strategies

In this study the validity of the methods provided for by Italian law (VDRL or RPR tests) were compared with the diagnostic strategy suggested by WHO (the use of VDRL and TPHA tests in parallel). Sensitivity, specificity and posterior probability of infection after a positive or a negative result were estimated. The application of two tests in parallel produces a statistically significant increase of sensitivity from 47% to 98% while the increase of proportion of false positives is not significant (from 15% to 16%). Probability of infection when the result is negative to the RPR is 0.07% while a negative result to the RPR and the TPHA tests has a probability to be really infected of 0.003%. The use of the two tests (RPR and TPHA) in parallel is able to give the highest degree of sensitivity, indispensable to select possible blood donors, while maintaining a good degree of specificity. The authors concluded that the use of VDRL alone does not exclude infectivity of a blood sample, and in accordance with WHO and international recommendations, the VDRL or RPR and TPHA tests should be used in parallel for syphilis screening.