Hepatitis B Virus - Genotyping

Hepatitis B virus has ten established genotypes, A through J, defined by more than 8% whole-genome nucleotide variation. Genotypes show distinct geographic distributions (for example A–D are widespread; B and C in Asia; E in West Africa; F in the Americas) and influence disease severity, progression and antiviral response, so genotype testing can guide prognosis and treatment.

HBV genotype testing is performed on a blood sample (serum or plasma) using molecular methods. Viral DNA is extracted, amplified by PCR, then genotyped by sequencing (Sanger or NGS) or genotype‑specific assays (line‑probe, real‑time PCR). Sequence-based phylogenetic comparison assigns genotypes A–J. Clinicians order genotyping for treatment choices, prognosis and epidemiology in chronic hepatitis B.

In India, hepatitis B virus genotype D is the most common. Genotype A occurs particularly in northern and western regions; genotypes C and B are less frequent, reported in eastern and northeastern areas. Mixed and recombinant infections are occasionally identified. Genotype can affect disease progression and response to antiviral therapy, so regional genotype data help guide clinical management.

The test for hepatitis B viral DNA is a quantitative HBV DNA PCR (real-time PCR) assay, commonly called the viral load test. It detects and measures hepatitis B virus DNA in blood (plasma/serum) to assess viral replication, guide treatment decisions, monitor response to antiviral therapy, and detect resistance. Results are reported in international units per milliliter (IU/mL).

The four main hepatitis B viral markers are HBsAg (surface antigen), anti-HBs (surface antibody), anti-HBc (core antibody — IgM indicates recent infection), and HBeAg (envelope/“e” antigen indicating high infectivity). These tests distinguish acute vs chronic infection, immunity, and viral replication, and guide monitoring and treatment decisions. Clinicians choose combinations based on clinical context.

Blood group B positive has an ABO genotype of either BB (B/B) or BO (B/O), because B is dominant over O. For the Rh factor, positive indicates either DD or Dd (D = RhD antigen dominant; d = Rh‑negative). So someone B+ is genetically B/B or B/O combined with D/D or D/d.