Sensitivity and specificity of capillary blood HBsAg as a surrogate marker for HBeAg in pregnant women

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Abstract
Infants at high risk of acquiring hepatitis B virus (HBV) infection from their hepatitis B e antigen (HBeAg)‐positive mothers are prime targets for early HBV immunization. The usefulness of fingerprick blood of pregnant women as a surrogate marker to identify infants who would need immunization soon after birth was evaluated. Using HBeAg from venous blood as the standard, the detection of hepatitis B surface antigen (HBsAg) by reverse passive haemagglutination in capillary blood yielded an overall sensitivity of 97% and a specificity of 96% for detecting HBeAg at a cutoff titre of 22.5. Pregnant women with a capillary HBsAg titre of 22.5 or greater are 24 times more likely to infect their babies, while the chances of transmitting HBV infection with a titre lower than the cutoff point are almost nil. When the cost of HBV vaccine eventually comes down to levels suitable for public health use, a cutoff titre of 22.5 is suggested in order to identify infants who should be vaccinated soon after birth.