Hepatitis serology interpretation is a core competency for clinicians in many fields: gastroenterology, hepatology, infectious diseases, sexual health, obstetrics (HBV screening in pregnancy), occupational health (healthcare worker screening), and primary care. The markers for HBV are numerous and each tells a different part of the story: what happened to this person, what their current immune status is, whether they have active infection or immunity, and whether they are infectious to others.
Hepatitis B Serology: The Markers Explained
HBsAg (Hepatitis B surface antigen): the viral envelope protein. HBsAg positive means the HBV virus (or its surface antigen, as HBsAg can be produced in large excess) is present. Persistent HBsAg for more than 6 months defines chronic hepatitis B infection. HBsAg is the primary screening test for HBV infection.
Anti-HBs (antibody to HBsAg): protective neutralising antibody. Anti-HBs positive (above 10 mIU/mL) means immunity, either from natural infection (accompanied by anti-HBc) or from vaccination (anti-HBs without anti-HBc). The vaccination target is anti-HBs above 100 mIU/mL after the primary course.
HBcAg (Hepatitis B core antigen): the viral nucleocapsid protein. HBcAg is not detected in serum (it remains inside the virion) and is not used as a serum test.
Anti-HBc (antibody to core antigen): an antibody against HBcAg. Anti-HBc total (IgM + IgG) is positive in natural infection (both past and current) but NOT in vaccinated individuals (vaccination induces anti-HBs only, not anti-HBc). Anti-HBc IgM specifically: positive in acute HBV infection. The anti-HBc IgM/IgG ratio helps distinguish acute from chronic infection.
HBeAg (Hepatitis B e antigen): a secreted protein derived from the pre-core/core gene. HBeAg positive indicates active HBV replication and high viral load (typically HBV DNA above 10^7 to 10^9 IU/mL). HBeAg is a marker of high infectivity. HBeAg seroconversion to anti-HBe (loss of HBeAg, appearance of anti-HBe) generally indicates reduction in viral replication and is a treatment target in chronic HBV.
HBV DNA (viral load): quantitative PCR measuring circulating HBV genome copies. The gold standard for measuring replication level and treatment response. Expressed in IU/mL. Detectable HBV DNA below the HBeAg threshold defines "pre-core/core promoter mutant" HBeAg-negative chronic hepatitis B, which can have active inflammation despite HBeAg negativity.
Common HBV Serological Profiles and Their Interpretation
Susceptible (never infected, not vaccinated): all markers negative.
Acute HBV infection: HBsAg positive, anti-HBc IgM positive, HBeAg positive (high replication phase). Most adults (more than 95 per cent) clear acute HBV spontaneously.
Chronic HBV infection, HBeAg-positive (immune tolerant or immune active phase): HBsAg positive, anti-HBc total positive, HBeAg positive, HBV DNA positive (high, typically above 10^6 IU/mL). HBeAg-positive chronic HBV in immune active phase has significant necroinflammation and progressive liver disease; treatment is indicated.
Chronic HBV infection, HBeAg-negative: HBsAg positive, anti-HBc positive, HBeAg negative, anti-HBe positive, HBV DNA positive (often fluctuating, 10^3 to 10^7 IU/mL). Pre-core or core promoter mutations allow continued replication without HBeAg secretion. Active liver disease possible despite HBeAg negativity; treatment decision based on HBV DNA level, ALT, and liver histology.
Resolved HBV infection (naturally acquired immunity): HBsAg negative, anti-HBc positive, anti-HBs positive. The person had natural HBV infection in the past, cleared it, and has protective immunity.
Vaccine-induced immunity: HBsAg negative, anti-HBc negative, anti-HBs positive (above 10 mIU/mL). No evidence of natural infection; immunity from vaccination only.
Isolated anti-HBc (core antibody alone): HBsAg negative, anti-HBc positive, anti-HBs negative. Seen in: remote resolved infection with waned anti-HBs, occult HBV infection (low-level HBsAg below detection threshold with detectable HBV DNA), false-positive anti-HBc (rare). Clinically important before immunosuppression or bone marrow transplantation as reactivation risk.
Hepatitis C Serology and Diagnosis
HCV diagnosis uses a two-step approach:
Step 1: HCV antibody EIA (anti-HCV). Tests for IgG antibodies against HCV structural and non-structural antigens. A positive anti-HCV indicates exposure to HCV (past or current infection). Anti-HCV does not distinguish cleared from active infection and does not appear until approximately 8 to 12 weeks after exposure (the diagnostic window period). Point-of-care anti-HCV tests (finger-prick blood) have enabled community-based HCV screening in key populations.
Step 2: HCV RNA (viral load, qualitative or quantitative PCR). Detects and quantifies circulating HCV RNA. Positive HCV RNA confirms active (current) HCV infection. Negative HCV RNA in an anti-HCV-positive patient means: (a) past infection cleared spontaneously (approximately 20 to 30 per cent of those infected), (b) successfully treated and cured, or (c) the patient is in the pre-seroconversion window and HCV RNA may become positive later.
Chronic HCV infection is defined as detectable HCV RNA for more than 6 months. Without treatment, approximately 20 per cent of those with chronic HCV develop cirrhosis within 20 years, and 1 to 4 per cent per year of those with cirrhosis develop HCC.
HCV genotype: HCV has 8 genotypes (1 through 8) with distinct geographic distributions. Historically, genotype influenced treatment choice and duration. Modern pan-genotypic direct-acting antivirals (sofosbuvir-velpatasvir and others) are highly effective (sustained virological response, SVR, above 95 per cent) across all genotypes, reducing the clinical importance of genotyping for treatment selection.
Frequently Asked Questions
What is HBsAg and what does a positive result mean?
HBsAg (Hepatitis B surface antigen) is the surface protein of the hepatitis B virus. A positive HBsAg means HBV (or excess HBsAg) is present in the blood. If HBsAg remains positive for more than 6 months, the person has chronic hepatitis B infection.
What does anti-HBs positivity mean?
Anti-HBs (antibody to HBsAg) positivity means protective immunity to HBV. A level above 10 mIU/mL indicates immunity. It can result from natural infection (in which case anti-HBc is also positive) or from vaccination (in which case only anti-HBs is positive, no anti-HBc).
How do I interpret an isolated anti-HBc result?
Isolated anti-HBc (anti-HBc positive, HBsAg negative, anti-HBs negative) occurs in: remote cleared infection with waned anti-HBs, occult HBV infection (low-level HBsAg below detection limits), or rarely, false-positive anti-HBc. This pattern is important to recognise in patients about to receive immunosuppressive therapy: reactivation of occult HBV can occur and prophylactic antiviral therapy is required.
What is HBeAg and why does it matter?
HBeAg (Hepatitis B e antigen) is a marker of active HBV replication. HBeAg-positive patients have high viral loads (typically above 10^7 IU/mL) and high infectivity. HBeAg seroconversion (loss of HBeAg, gain of anti-HBe) is a key treatment endpoint in chronic hepatitis B, indicating reduced replication and lower risk of progression.
What is the difference between past infection and vaccine immunity for HBV?
In vaccinated individuals: anti-HBs positive, anti-HBc negative (no marker of natural infection). In past natural infection with immunity: anti-HBs positive, anti-HBc positive (natural infection always induces anti-HBc, vaccination does not). This distinction is important for occupational health screening and blood safety assessment.
What is anti-HCV and does it mean someone currently has hepatitis C?
Anti-HCV is an antibody to hepatitis C virus that appears approximately 8 to 12 weeks after exposure and remains positive for life, regardless of whether infection is current or cleared. Anti-HCV positivity does not confirm active infection. HCV RNA (viral load) testing is required to determine whether infection is active (RNA positive) or cleared (RNA negative).
What is SVR in hepatitis C?
Sustained Virological Response (SVR, SVR12) is defined as undetectable HCV RNA at 12 weeks after completing hepatitis C treatment. SVR is considered a cure: over 99 per cent of patients who achieve SVR12 remain HCV RNA-negative long-term. Modern direct-acting antiviral regimens achieve SVR12 rates of 95 to 99 per cent.
What are direct-acting antivirals (DAAs) for hepatitis C?
DAAs are oral antiviral drugs that directly target specific steps in the HCV replication cycle: NS5B polymerase inhibitors (sofosbuvir), NS5A inhibitors (velpatasvir, ledipasvir, daclatasvir), and NS3/4A protease inhibitors (glecaprevir, grazoprevir). Pan-genotypic DAA combinations (e.g., sofosbuvir/velpatasvir, glecaprevir/pibrentasvir) cure HCV across all genotypes in 8 to 12 weeks with minimal side effects.
What is occult hepatitis B?
Occult hepatitis B is HBV infection characterised by HBsAg negativity (below detection threshold) with detectable HBV DNA in liver and/or serum. Anti-HBc is typically positive. Occult HBV can reactivate to overt infection under immunosuppression (chemotherapy, rituximab, corticosteroids, solid organ transplant). Antiviral prophylaxis with tenofovir or entecavir prevents reactivation.
Why is HBV vaccination incomplete protection without anti-HBs testing?
HBV vaccination induces anti-HBs in approximately 90 to 95 per cent of healthy immunocompetent adults. Approximately 5 to 10 per cent are non-responders or hypo-responders, particularly those who are obese, elderly, immunocompromised, or smokers. Anti-HBs testing 4 to 8 weeks after the final vaccine dose is required to confirm protective response. Non-responders require revaccination (double dose or additional doses) and, if still non-responding, HBV immune globulin (HBIG) as post-exposure prophylaxis.