Discrepant HBsAg Test Results In Pregnant Women Screened to Identify Infants at Risk for Perinatal Hepatitis B Virus Infection

Background: 90% of hepatitis B virus (HBV) perinatally infected infants develop chronic infection, with 25% at risk of premature death from liver failure or cancer. Timely post-exposure prophylaxis (PEP) with hepatitis B vaccination and immune globulin prevents 85% - 95% of perinatal infections among high-risk infants. All pregnant women in the U.S. are screened for hepatitis B surface antigen (HBsAg) to identify infants at risk for perinatal HBV infection.  A second prenatal HBsAg test is performed for women at risk of HBV infection or by state law requirement. Resolution of discrepant HBsAg laboratory results (first positive, then negative) is necessary to ensure appropriate PEP. 

Objectives: To identify HBsAg discrepant results and determine factors contributing to those discrepancies.

Methods: Information on discrepant HBsAg test results (positive followed by negative result) was collected through passive reports from local and state Perinatal Hepatitis B Prevention Program Coordinators starting April 1, 2009. Information on demographics, hepatitis B surface antigen (HBsAg) tests, confirmatory tests, additional hepatitis B serologies (including antibody to hepatitis B core antigen [HBcAb] and HBV DNA), other chronic maternal infection, and hepatitis B vaccination dates were collected on a standard form.

Results: From April 2009-June 2010, 48 sets of discrepant HBsAg test results were passively reported. Ten (21%) lacked sufficient information to determine the reason for discrepancy. Of the remaining 38, 36 (95%) were false-positive based on results of additional serologic markers [30 (83%) HBcAb undetected, 2 (6%) HBsAb detected and 4 (11%) HBV DNA undetected]; 1 (3%) initial positive was close to the signal to cut-off level; and 1 (3%) was due to technical error.

Conclusions: Testing for HBcAb was the most useful test to resolve discrepancies.