Hepatitis B serology interpretation

I have struggled with Hepatitis B serology interpretation for a long time. I am trying to learn it properly for the exam, and also it is a common infection. In Australia, around 1 % of the population has Hepatitis B.

Key point:

- We are testing for 2 things here. One is antibody and one is antigen.

- Diagnostic test: To diagnose Hepatitis B. Only need to order 3 tests.

1. Hepatitis B surface Antigen: The presence of Hepatitis B surface antigen indicates infection.
2. Hepatitis B core antibody: The presence of antibodies to Hepatitis B core antibody indicates past infection or current infection. 
3. Hepatitis B surface antibody: present after vaccination and resolved infection.

- The following is a table which summarises the interpretation of the test results:

- How I remember this is that I remember HbsAg as a thief, anti-HBc as a security guard and anti-HBs as the policeman. HBsAg means the thief is in the shop and it means infection. When the thief is caught by the security guard (anti-HBc), the problem is still not solved completely until the policeman arrives (anti-HBs). If the policeman is there (anti HBs), no thief will come in and indicates immunity.

- Markers of hepatitis B virus infection : HBV antigens and host antibodies, HBV DNA and genotype, biochemical markers, and the degree of hepatic fibrosis and inflammation. 

- HBeAg: it promotes persistent infection 

- Antibody to e-antigen: not a protective antibody but its presence indicates better immunological control.

- HBV DNA

- ALT: indications for liver damage. Recent studies have shown that normal range of ALTs are <30 in men and < 19 in women 

- The following picture summarises the 4 phases to treatment decisions

- Immune tolerance: The immune tolerance phase is characterised by hepatitis B e antigen (HBeAg) positivity, high HBV DNA levels (>20,000 IU/mL, and commonly over 1 million IU/mL), normal ALT levels and minimal level liver injury. During this phase, which may persist for decades, liver inflammation or fibrosis is either absent or minimal. This phase is associated with a low risk of progression to advanced liver disease, and it is thought to occur most commonly in those who acquire the infection vertically from HBeAg-positive mothers. 

- Immune clearance phase: the immune clearance phase is also called the immune competent or active phase. The liver injury in HBV is determined by the immune response to the virus. The host's immune system recognises the HBV as foreign, and mounts a cytotoxic response to infected hepatocytes. This phase is characterised by fluctuating HBV DNA and ALT levels. Recurrent bouts of active inflammation and , eventually, fibrosis can occur int he liver following these repeated immune 

Mediated attacks. An important outcome of this phase is the seroconversion of HBeAg to anti-heb, which is associated with a lower level of viraemia. The observed rate of clearance of HBeAg in those with or without elevated ALT levels averages 8%-12% per year. However, a number of people will still develop active liver disease after HBeAg seroconversion, generally owing to immune escpape; that is, emergency of HBV mutant variants, particularly the core or preacher mutation that renders the virus unable to encode for HBeAg.

Reference:

Hepatitis B for GP