How to test for hepatitis D virus infection: evidence and rationale to inform policy recommendations and future...

Chronic hepatitis D virus (HDV) coinfection in people with chronic hepatitis B is associated with rapid progression to liver cirrhosis and high mortality. In 2020, the estimated global HDV burden among people with chronic hepatitis B was 12 million people, with a seroprevalence of 4·5%. Treatment options are now evolving with the introduction of bulevirtide; however, testing for HDV remains very low. In 2024, WHO published comprehensive guidelines on the management of people with chronic hepatitis B, including recommendations for the first time on who to test and how to test for HDV infection. WHO recommends an anti-HDV serological assay for those with chronic hepatitis B, and if reactive, an HDV RNA test to confirm active infection and, where available, reflex laboratory-based testing for anti-HDV in those who are HBsAg positive and an HDV RNA test in those who are anti-HDV positive. WHO also recommended universal anti-HDV testing among all individuals who are HBsAg positive, or a risk-based approach among populations at high risk when this is not feasible. We present two complementary Reviews-one on who to test and one on how to test for HDV infection. This Review on how to test provides a comprehensive landscape and performance review of available serological and molecular diagnostic assays, as well as the evidence and rationale for the adoption of reflex testing both for anti-HDV in individuals who are HBsAg positive, and HDV RNA testing in those who are anti-HDV positive. Key implementation considerations and research priorities include the need for countries to incorporate HDV testing into their national policies and guidelines for chronic hepatitis B, expand laboratory capacity and training that leverages existing networks and infrastructure, promote access to quality diagnostics, including anti-HDV rapid diagnostic tests, and conduct evaluations of quality-assured assays using all HDV genotypes.