Virology Question and Answer Scheme (VIROQAS)
The importance of being earnest: Following up a low level hepatitis B surface antigen (HBsAg) result

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Case description

A 24 yr old Lithuanian woman (LA) resident in Ireland presented to the antenatal service of her local (regional) hospital for the first time at 36 weeks gestation in July 2008. Blood was drawn (sample date 08/07) and sent to the National Virus Reference Laboratory (NVRL) for antenatal screening for evidence of infection with human immunodeficiency virus (HIV), hepatitis B virus (HBV), and hepatitis C virus (HCV). The sample was weakly positive in the HBsAg Abbott Architect (reading/cut-off:

Discussion

This case highlights the importance of follow-up testing when a weak positive HBsAg result is generated: of particular importance is the requirement to perform anti-HBc investigation even if HBsAg is not detected on follow-up. If the first and final samples in this case were tested for HBsAg only, it is probable the patient would not have been identified as HBV infected. Whilst it is unusual HBeAg was not detected in this case, this may have been detectable for a short time between samples 4

Conclusion

This case illustrates the importance of not dismissing weakly positive HBsAg results, and raises the issue of whether HBV DNA testing should be routinely performed in this patient cohort with limited serological evidence of HBV infection. The use of serological assays – even those that are highly sensitive and specific – is compromised by the generation of false-positive results especially when testing low-risk populations, e.g., in national screening programmes.12 In the case presented here,

Competing interest

None declared.

Ethical approval

Not required.

Funding

None.

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