THE USE OF DRIED BLOOD SPOTS FOR MEASURING THE IMMUNITY AGAINST HBV: THE SIGNIFICANCE OF ANTIBODY DILUTION

Background: Dried blood spots (DBS) have been used to study the prevalence of hepatitis B virus (HBV) infection in endemic areas and in high-risk groups. However, detection of HBV serological markers in DBS by ELISA assays has not yet been fully optimised. The aim of the present study is to evaluate the dilution level of anti-HBs when DBS cards are used as storage matrix implemented for ELISA. Material and methods: Antibodies against hepatitis B surface antigen (anti-HBs) were detected by ELISA. The following specimens were examined: serum samples from 20 patients paired with 20 DBS; serum samples from 20 HBV-vaccinated healthcare workers paired with 20 dried serum spots (DSS); and four different dilutions of Immunovenin. Different elution protocols were used in order to study the problem with sample dilution. Results: Specificity of 100% and sensitivity of 45% were established for DBS versus the “gold standard”. Dilution of the eluted DBS/DSS samples was established and in some cases the measured anti-HBs titre dropped under 10 mIU/ml. Correlation was not observed between the positive initial anti-HBs serum titres and the obtained values of DBS/DSS testing. Also, 20- to 50-fold dilutions were measured for eluted DSS samples when testing Immunovenin. Increasing of the eluted sample concentration raised DSS anti-HBs titre. Conclusions: In order to resolve the problem of dilution, it is necessary to validate different elution protocols because the small amount of sample in DBS showed lower titres.