Hepatitis D Virus (HDV) RNA, PCR

The Hepatitis D Virus (HDV) RNA, PCR assay is used to document active HDV infection (delta hepatitis) in HBsAg‑positive patients and to separate ongoing viremia from past infection when HDV serology is reactive. The test supports classification of HDV coinfection versus superinfection, informs the evaluation of severe or fulminant hepatitis in persons with hepatitis B, assists in assessing progression of chronic liver disease in HBV carriers, and is used to monitor virologic response during and after antiviral treatment. Synonyms commonly used include HDV PCR and HDV RNA.

Hepatitis D virus is a circular, single‑stranded RNA virus that is replication‑defective and requires hepatitis B surface antigen (HBsAg) from hepatitis B virus to form its envelope; without HBV, HDV cannot complete its replication cycle. Three principal genotypes show geographic clustering and differ in clinical severity: genotype 1 is encountered worldwide, genotype 2 predominates in East Asia, and genotype 3 is largely reported from South America. Transmission is chiefly parenteral, with sexual and vertical routes less frequent. Higher‑risk groups include people who inject drugs, transplant recipients, patients on hemodialysis, and those receiving repeated blood component transfusions. Infection occurs either as coinfection with HBV or as superinfection of an existing HBsAg carrier. Coinfection typically has a 3–7 week incubation period, often produces an acute illness with biphasic aminotransferase peaks (initially from HBV, followed by HDV), and resolves in most cases. Superinfection on chronic HBV rarely clears spontaneously (approximately 5%–10%) and more commonly progresses to chronic hepatitis and cirrhosis, with a higher risk of hepatic failure; a direct causal association with hepatocellular carcinoma has not been proven. Differentiation of coinfection from superinfection relies on the clinical course and HBV serology: anti‑HBc IgM supports coinfection, whereas an anti‑HBc IgG pattern favors superinfection. In transplant settings, infection confined to hepatocytes may persist when HBV is absent or suppressed, leading to undetectable viremia. Nucleic acid testing for HDV RNA is analytically sensitive and specific and can reveal viremia within days of infection, preceding the appearance of HDV antibodies by weeks. Accordingly, HDV RNA testing is useful for early diagnosis and for tracking virologic activity over time.