Low-level hepatitis B surface antigen by ECLIA stratifies early relapse risk in patients with interferon-based HBV...

Current definitions of functional cure in chronic hepatitis B (CHB) rely on conventional assays of HBsAg tested by enzyme-linked immunosorbent assay (ELISA-HBsAg), which may misclassify patients with low-level residual antigenemia as cured, leading to relapse after treatment cessation. This study aims to investigate whether high-sensitivity electrochemiluminescence immunoassay of HBsAg (ECLIA-HBsAg) can provide a much better definition of deep functional cure in CHB patients discontinuing interferon (IFN) add-on therapy.

This retrospective study included 292 CHB patients reaching interferon-induced functional cure with HBsAg tested by ELISA and conducted a 48-week follow-up. Clinical-virological data were collected at treatment cessation and during follow-up. HBsAg were measured by ELISA and ECLIA, simultaneously. LASSO-Cox regression was used for predictor selection. Model performance was evaluated using time-dependent ROC curves, calibration analysis, and decision curve analysis (DCA). The optimal cutoff was determined via maximally selected rank statistics.

During a 48-week follow-up, 24 patients (8.2%) in total relapsed. Cumulative relapse rates at 12, 24, 36, and 48 weeks were 1.4%, 3.8%, 6.2%, and 8.2%, respectively. ECLIA-HBsAg emerged as the sole independent predictor (HR: 9.32, 95% CI: 4.97-17.47, p<0.001), with an optimal cutoff of 0.38 COI. Patients with ECLIA-HBsAg >0.38 COI exhibited a significantly higher relapse risk (p=0.0029). The model demonstrated strong discrimination (C-index: 0.805; AUCs at 24/36/48 weeks: 0.790, 0.789, and 0.768, respectively) and high clinical utility.The mean lead-time gain of ECLIA-HBsAg over ELISA-HBsAg was 28 weeks in functional relapsers (95% CI: 20.5-35.5 weeks, p < 0.001).

Patients who experience relapse under conventional ELISA definitions often harbor residual HBsAg detectable by high-sensitivity testing. Based on an exploratory cutoff of 0.38 COI, we propose that highly sensitive ECLIA might be incorporated into clinical practice as a new, more stringent standard for defining "deep functional cure".