Screening of blood donors for the presence of markers of infection with hepatitis B and C viruses is one of the main provisions to prevent the spread of these serious human pathogens. The incidence of acute hepatitis B declined significantly during the last 15 years and was 6.2 cases per 100 000 population in 1999. The age structure of acute viral hepatitis B is also changing. The prevalence of carriers of HBsAg in the general population declined also and in 1996 it was 0.66%. The incidence of acute hepatitis C is rising and was 3.2 cases per 100 000 population in 1999. The prevalence of anti-HCV in the population of the Czech Republic is not known. From 1993 data are available on the number of donors and primary donors eliminated on account of HBV and HCV markers. The annual relative numbers of primary donors eliminated on account of HBV are most frequently within the interval of 0.2 - 0.3%, on account of HCV 0.6 - 0.8 % with a more marked decline in 1999. Reactive findings of HBsAg with anti-HCV during screening of blood donors are confirmed according to the mentioned procedures in the National reference laboratory for viral hepatitis. From the analyzed group of 722 samples sent for confirmation of anti-HCV only in 55.1% of samples values of the reactivity during the initial screening in laboratories of the transfusion service were given. The results of the initial screening of these samples were in 77.4% reactive, in 13.6% in the „gray zone“ (S/CO 0.8-1.0) and in 9% of the samples negative (with S/CO values of 0.7-0.8 in the majority). The results of the confirming examination of 722 specimens were in 13.6% positive, in 57.5% negative and in 28.9% not unequivocal. In the confirming exa minations the authors included also assessment of HBV DNA and HCV RNA as supplementary examinations. Compre- hensive confirming examinations using several methods lead to a more reliable, more standardized and more effective confirmation of the specificity of screening examinations of HBsAg and anti-HCV.

        Key words: hepatitis B, hepatitis C, blood donors, confirmation, prevalence