Resolving Uncertainty in Hepatitis B Diagnosis: Evaluating Neutralization Testing for Borderline HBsAg.

Objective: To assess the performance of neutralization confirmatory testing for borderline hepatitis B surface antigen (HBsAg) results (signal-to-cutoff [S/CO] 1.0-10.0) in a low-prevalence population.

Method: We retrospectively analyzed 115 borderline-reactive HBsAg samples from asymptomatic adults with normal liver enzyme levels. Screening was performed using the Abbott Alinity i assay, followed by confirmatory testing with the Abbott HBsAg Confirmatory Reagent. A ≥50% signal reduction was required for confirmation.

Results: Among 115 borderline samples, 61 (53.0%) were confirmed by neutralization testing. Confirmation rates increased with higher S/CO values: 31.6% (1.0-2.0), 57.1% (2.1-5.0), and 75.0% (5.1-10.0). The median S/CO values were 1.5 (1.0-2.0), 3.4 (2.1-5.0), and 7.2 (5.1-10.0) for each subrange. Logistic regression showed a significant correlation between higher S/CO values and confirmation (odds ratio 1.42 per unit increase, p<0.001). Notably, most unconfirmed cases had S/CO values below 3.0, suggesting frequent false reactivity in low-positive samples.

Conclusion: Lower borderline HBsAg results often reflect nonspecific assay reactivity, emphasizing the need for confirmatory testing to prevent misdiagnosis. Higher S/CO values were strongly associated with true HBsAg positivity, supporting the use of neutralization testing in routine practice.