Cut-off value setting of enzyme-linked immunosorbentassay reagents for detection of hepatitis B surface antigen in blood screening

  Objective  To explore the necessity and range of grey area of enzyme-linked immunosorbent assay (ELISA) reagents for detection of hepatitis B surface antigen (HBsAg).

  Methods  HBsAg positive sero-panels(423 copies) and HBsAg negative blood donors (2 996 copies) were detected by domestic reagent and imported reagent in parallel, and the sensitivity, specificity of the reagents under different absorbance value/threshold value(S/CO) ratio were calculated, and Yoden index was used to analyze the rationale range of grey area of two reagents.

  Results  When the S/CO ratio was 0.4, the domestic reagent had the largest index(0.957), and the imported reagent had the largest index(0.971) when the S/CO ratio was 0.7.

  Conclusion  If HBsAg of the blood donor is tested for 1 time by ELISA reagents, it is necessary to set the gray zone for reagents in our laboratory. The cut-off value should be 0.4 and above for domestic ELISA kits, while ≥0.7 for imported kits.