Nationwide Implementation of Double Reflex Testing for Hepatitis Delta in Spain: Results From the Retrospective Phase of the Spain-DDR Study

Abstract

BACKGROUND: Hepatitis delta virus accelerates liver disease progression in chronic hepatitis B, yet remains underdiagnosed. Guidelines recommend double reflex diagnostic testing with antibody testing followed by viral load testing, but uptake remains inconsistent. AIMS: To evaluate double reflex diagnostic implementation in Spain during the retrospective phase of the Spain Double Reflex Diagnostic study. METHODS: Nationwide, multicenter retrospective analysis of individuals positive for hepatitis B surface antigen (2022-2024) from 80 centers. Laboratory data included hepatitis B surface antigen, hepatitis delta virus antibody and hepatitis delta virus viral load. Uptake rates, hepatitis delta virus antibody positivity, viral load confirmation and viral load-confirmed prevalence were calculated with 95% confidence intervals. RESULTS: Among 65,763 individuals positive for hepatitis B surface antigen, hepatitis delta virus antibody testing uptake increased from 55.1% (54.4-55.8) in 2022 (n = 18,986) to 72.5% (71.9-73.1) in 2023 (n = 22,463) and 85.8% (85.1-86.4) in 2024 (n = 24,314; p < 0.0001). Antibody positivity remained stable (5.6%, 4.9%, 5.3%). Viral load confirmation among antibody-positive patients improved from 72.6% in 2022 to 90.8% in 2023 and 91.0% in 2024. Viral load-confirmed prevalence among antibody-positive individuals was 40.3% in 2022, 31.6% in 2023, and 30.1% in 2024. Regional heterogeneity was marked, with several autonomous communities achieving near-universal uptake (> 95%). CONCLUSION: Between 2022 and 2024, double reflex diagnostic implementation expanded rapidly, demonstrating national feasibility and describing hepatitis D virus seroprevalence. However, regional inequities persist. Sustained uptake will require standardised reflex protocols, harmonization of viral load assays and continuous training to reduce underdiagnosis and improve care of coinfected patients.