Hepatitis B Serology and Viral Load

Hepatitis B virus (HBV) is a DNA virus that infects hepatocytes. Serology detects viral antigens (HBsAg, HBeAg) and the host antibodies (anti-HBs, anti-HBc IgM and total, anti-HBe), and a quantitative HBV DNA test measures viral replication. The pattern defines acute infection, chronic infection, resolved infection, immunity after vaccination and occult infection. Together with alanine aminotransferase (ALT), HBV DNA and liver fibrosis assessment, it directs treatment and surveillance.

About 254 million people have chronic hepatitis B, with 1.2 million new infections and 1.1 million deaths a year from cirrhosis and hepatocellular carcinoma. Prevalence is highest in sub-Saharan Africa and the Western Pacific (over 6%). Infection acquired at birth or in early childhood becomes chronic in 90% and 30% respectively, compared with under 5% in adults. About 15 to 40% of untreated chronic carriers develop cirrhosis or liver cancer.

Indications. Jaundice, raised transaminases, suspected acute hepatitis, screening of pregnant women, blood donors, healthcare workers, household and sexual contacts, people from high prevalence regions, people with HIV or hepatitis C, those on dialysis, people who inject drugs, and before immunosuppressive or biological therapy and chemotherapy (to prevent reactivation). Also vaccine response testing in healthcare workers and infants of infected mothers.

Specimen. Serum or plasma, 3 to 5 mL, no fasting needed. Stable for several days at 2 to 8 °C. HBV DNA in plasma separated within 6 hours or serum, and frozen if delayed.

Serological markers.

• HBsAg: appears 1 to 10 weeks after exposure (before symptoms), and persistence over 6 months defines chronic infection.
• Anti-HBs: protective antibody. A level of 10 mIU/mL or more indicates immunity after vaccination or recovery.
• Anti-HBc IgM: marks acute or recent infection (up to 6 months), and may reappear in flares of chronic infection.
• Anti-HBc total (IgG): marks past or present infection, and is not present after vaccination.
• HBeAg: marks high replication and infectivity. Anti-HBe: seroconversion, usually lower replication.
• HBV DNA: quantitative, in IU/mL.

Interpretation of common patterns.

Phases of chronic infection.

• Immune tolerant: HBeAg positive, HBV DNA over 10^7 IU/mL, normal ALT, minimal liver damage. Common in those infected at birth.
• Immune active (HBeAg positive): HBeAg positive, HBV DNA over 20 000 IU/mL, raised ALT, active inflammation. Treatment is considered.
• Inactive carrier: HBeAg negative, anti-HBe positive, HBV DNA under 2000 IU/mL, normal ALT. Low risk, with monitoring.
• HBeAg-negative chronic hepatitis: HBeAg negative, HBV DNA over 2000 IU/mL, raised ALT, active disease from precore or core promoter mutants. Treatment is considered.
• Resolved infection: HBsAg negative, anti-HBc positive, with or without anti-HBs, and with HBV DNA undetectable or very low (occult HBV).

Treatment endpoints and thresholds. Treatment is generally considered when HBV DNA is over 2000 IU/mL with ALT over the upper limit and fibrosis (F2 or more, or cirrhosis), or in cirrhosis with any detectable DNA, in immunosuppression, and in HBV with HIV coinfection. Antiviral drugs (tenofovir, entecavir) suppress DNA to undetectable in over 95% of adherent patients. Loss of HBsAg (functional cure) occurs in 1 to 2% a year on treatment.

Monitoring. ALT and HBV DNA every 3 to 6 months in treated or active patients, every 6 to 12 months in inactive carriers. HBsAg quantification may help. Hepatocellular carcinoma surveillance with ultrasound (with or without alpha fetoprotein) every 6 months in cirrhosis, in people from sub-Saharan Africa over 20 years, Asian men over 40 years and women over 50 years, and those with a family history of liver cancer. Fibrosis assessment with elastography or FIB-4.

Hepatitis D. Anti-HDV total antibody and HDV RNA in all HBsAg-positive people with severe or unexplained disease, since coinfection accelerates cirrhosis.

Critical values and findings needing immediate action.

• Acute hepatitis B with coagulopathy (INR over 1.5) or encephalopathy: acute liver failure, urgent transfer to a liver unit.
• HBsAg positive pregnant woman with high viral load (over 200 000 IU/mL): antiviral therapy from 28 to 32 weeks, and infant hepatitis B immunoglobulin and vaccine within 12 to 24 hours of birth.
• HBsAg positive or anti-HBc positive patient before chemotherapy, rituximab, high dose steroids or other immunosuppression: antiviral prophylaxis to prevent reactivation, which can cause fatal liver failure.
• Flare with ALT over 10 times the upper limit and rising bilirubin.
• Cirrhosis with HBV DNA detectable: start antiviral treatment.
• Needle stick exposure in a non-immune person: hepatitis B immunoglobulin and vaccine.

Interferences and pitfalls.

• Isolated anti-HBc needs HBV DNA, since occult infection can reactivate under immunosuppression.
• HBsAg may be negative in the window between loss of HBsAg and appearance of anti-HBs, when anti-HBc IgM identifies acute infection.
• Vaccine escape and surface mutants may give false negative HBsAg assays.
• HBV DNA assays vary, and the same assay and units (IU/mL) are used for monitoring.
• ALT is normal in a proportion of patients with significant fibrosis, and in people over 30 years the normal limit is lower than traditional ranges (about 30 U/L in men and 19 U/L in women).
• HBeAg-negative chronic hepatitis can fluctuate, and one low DNA does not prove inactive disease. Three measurements over a year are needed.
• Anti-HBs wanes over time after vaccination, but immune memory persists, and booster doses are not needed in most immunocompetent people.
• Hepatitis B and D reactivation can follow direct acting antiviral treatment of hepatitis C, and stopping nucleos(t)ide drugs can cause flares.

Special groups.

• Newborns of HBsAg-positive mothers: immunoglobulin plus vaccine within 12 hours reduces transmission by over 90%. Test for HBsAg and anti-HBs at 9 to 12 months.
• Children: usually immune tolerant, with normal ALT and high DNA, and treated selectively.
• Pregnancy: screening is universal, and tenofovir is used to prevent transmission.
• HIV coinfection: tenofovir based treatment treats both viruses.
• Dialysis and immunosuppressed patients: poor vaccine response, higher dose or repeated schedule.
• Regions: high prevalence, with early childhood transmission, and limited access to HBV DNA testing and antivirals.

Follow up tests. HBV DNA, ALT and AST, full liver profile, INR, platelets, FIB-4 or elastography, ultrasound, alpha fetoprotein, HBeAg and anti-HBe, hepatitis D antibodies, hepatitis A and C serology, HIV test, liver biopsy in selected cases, kidney function and phosphate (tenofovir), and bone density.