Hepatitis B Virus Diagnosis Using Dried Blood Spots in the D.R. Congo: Overcoming Misdiagnosis to Achieve 2030 WHO Targets.

Background/Objectives: Hepatitis B remains a major public health concern in the Democratic Republic of the Congo (DRC). This study investigated HBV seroprevalence in Kinshasa and evaluated the diagnostic performance of rapid diagnostic tests (RDTs) compared with dried blood spot (DBS)-based immunoassays. Methods: DBS samples collected between 2016 and 2022 were transported to Spain for HBsAg and HBc-Ab testing using two chemiluminescence platforms (ECLIA-COBAS (Roche) and ELFA-miniVIDAS (bioMerieux)). A subset of participants also underwent on-site HBsAg screening using Determine™ (Abbott) RDTs. Results: Overall, active HBV infection was detected in 4.3% of participants and resolved infection in 14.3%, with no significant differences by age, sex, cohort, or HIV/HCV status. The RDT showed poor sensitivity (60% (95% CI: 26-88)) but high specificity (100% (95% CI: 98-100)), resulting in a 40% misdiagnosis rate. In contrast, DBS-based HBsAg immunoassays demonstrated excellent diagnostic accuracy, with both platforms achieving 100% sensitivity (ECLIA-COBAS 100%, 95% CI: 66-100; ELFA-miniVIDAS 100%, 95% CI: 99-100) and specificity (ECLIA-COBAS 100%, 95% CI: 98-100; ELFA-miniVIDAS 100%, 95% CI: 99-100). HBc-Ab detection showed platform-dependent variability, with lower sensitivity on ELFA-miniVIDAS (66% (95% CI: 46-82)) compared with ECLIA-COBAS (100% (95% CI: 96-100)). Predictive values were high across all assays, and inter-method agreement for HBsAg between RDT and chemiluminescence was good (Cohen's kappa 0.71, p < 0.001). Conclusions: These findings indicate moderate HBV transmission in Kinshasa and highlight the limited reliability of RDT-based screening. DBS proved to be a practical, robust, and scalable sampling method with outstanding diagnostic performance, making it well-suited for HBV testing in low-resource settings.