Understanding Hepatitis B Serology Results

Hi, this is Tom from Zero2Finals.com. I wanted to make a video about interpreting hepatitis B serology and this video is really concentrating on making it simple and easy so that you can really understand and remember how to interpret these results. This is a very popular exam topic and it quite often comes up in clinical practice as well so it's a useful skill to have and if you want more information on hepatitis in general, including the other viral hepatitises, then please go to Zero2Finals.com slash hepatitis. But let's get straight in. Firstly, it's essential to have a very basic understanding about antibodies otherwise you'll find it extremely hard to understand hepatitis B serology. Antibodies are basically proteins that are produced by B cells and there's millions of types of antibodies and each B cell only produces a single type of antibody and this single type of antibody only targets a single type of protein. The protein that's targeted by an antibody is called an antigen. The antigens could be proteins that are part of or cancers or even the body's own cells in the case of autoimmune disease and the job of antibodies is to go hunting for their specific antigens and when they find them they attach themselves to that antigen and then they help the rest of the immune system to launch an attack on whatever that antigen is and whatever the antigen is related to. In the case of hepatitis B there are antigens that are part of the hepatitis B virus and these are hepatitis B viral proteins. So let's start by introducing the antigens that are part of the hepatitis B virus and then talking about the relevant tests to these antigens. So there's three antigens that I want to talk about on the hepatitis B virus. The surface antigen, the E antigen and the core antigen. The surface antigen, which is what we call the hep B surface antigen, is found on the surface of the hepatitis B virus. If we find that the hepatitis B surface antigen is in the blood, if the hepatitis B surface antigen is positive, then we know that the person is infected with hepatitis B. If there's no hepatitis B infection then the virus wouldn't be releasing the surface antigen into the blood so you'd get a negative result. It's important to know that the vaccination for hepatitis B involves injecting the person with hepatitis B surface antigen. So what happens is the immune system creates a response to this hepatitis B surface antigen and then the person becomes immune to hepatitis B. If you test somebody after they've had the hepatitis B vaccine then they'll be positive for hep B surface antigen because that's what you injected into the person's body until the immune system responds and clears that antigen and then they'll have a negative result after that. The next antigen to talk about is the hepatitis B E antigen. The hep B E antigen is found between the core and the surface of the hepatitis virus and it floats in this space in between the two and it's released during replication of the virus and remember E antigen escapes, so E for escape, during replication. Therefore if you find the hep B E antigen is present it implies the patient has an acute phase of the infection where the virus is replicating very quickly. So the level of the hep B E antigen correlates with their infectivity because the virus is replicating very quickly. If a person becomes exposed to that patient's blood then they've got a high chance of becoming infectious. So if the hep B E antigen is higher they're more infectious to others. Finally we need to talk about the hepatitis B core antigen. This is found on the inside of the hepatitis B virus, on the core area of the hepatitis B virus. This antigen does not circulate in the blood so it's not a helpful test on a blood test because it will be negative either way. However it becomes relevant when we talk about antibodies. So next let's move on to talking about the antibodies and remember that antibodies are produced as part of the immune response and the B cells coming into contact with antigens and producing antibodies against those antigens. Just as there were three antigens involved in the hepatitis B virus there are also three antibodies that correspond to these antigens. So there's a surface antibody, an E antibody and a core antibody. So the hep B surface antibody demonstrates an immune response to the hep B surface antigen and remember the hep B surface antigen is given as part of the vaccine so somebody having a hep B surface antibody may simply indicate that they've been vaccinated and they've created an immune response to the vaccine. The hep B surface antibody may also be present in response to an infection. So if you have a hep B surface antibody you need to use the other viral markers to distinguish whether this is due to previous vaccine or whether it's Next let's talk about the hepatitis B E antibodies and remember that the hepatitis B E antigen implies that the patient is in an acute phase of the infection and the virus is replicating very quickly. E antigen escapes during replication. The level of the hepatitis B E antigen correlates with their infectivity but over time the immune system will respond to this antigen and start to produce antibodies and these are the hepatitis B E antibodies. When the hepatitis B E antigen is negative but the hepatitis B E antibody is positive this implies that they've been through a phase where the virus is replicating actively but the virus has now stopped replicating and the patient is less infectious because there's been a good immune response to the virus. Finally let's talk about the hepatitis B core antibodies. We also call these the hep B C antibodies. C for core and remember the hepatitis B core antigens are found on the middle of the virus and do not circulate in the blood. Hepatitis B core antibodies basically show an immune response to this antigen and they can help us distinguish between an acute chronic and a past infection and we can measure IgM versions and IgG versions of the hep B core antibody and remember that IgM generally is involved with acute infections and then IgG lingers after an infection and helps protect against that infection in the future. So when we look at hep B core antibodies the IgM version implies there's an acute infection and it will give a high titer so a high result if there's an acute infection and a low result if there's a chronic infection and then if the IgG is positive and the hep B surface antigen is negative, meaning that the person doesn't have an active infection and the hep B virus is not producing the surface antigen, then this indicates a past infection. The final thing to note is that there's a definitive test for the viral load of hepatitis B and this is you test for the hepatitis B DNA directly and this can be abbreviated to hep B virus DNA and this will give a direct count of the number of viral copies in the bloodstream and this number is often referred to as the viral load. A final note on how to test somebody you suspect may have hepatitis B, so when you want to screen somebody for hep B, test for the hep B core antibody which will test for a previous infection and test for the hep B surface antigen for active infection. If these are positive then test for the hep B antigen to see how infective they are and how much viral replication you're getting and then test for the hepatitis B DNA to look for the viral load to see how many viral copies there are in the bloodstream. One thing it's worth remembering if you don't remember anything else from this video is that the hepatitis B surface antigen is what's used in the vaccine, so a single hepatitis B surface antibody result that's positive may simply just mean that the person's previously been vaccinated as this is something that you might see coming up in your clinical practice and can make people panic until they realise it just means they're vaccinated. So thanks for watching, I hope you found this video helpful. If you did don't forget there's plenty of other resources on the zero to finals website including loads and loads of notes on various different topics that you might cover in medical school with specially made illustrations. There's also a whole test section where you can find loads of questions to test your knowledge and see where you're up to in preparation for your exams. There's also a blog where I share a lot of my ideas about a career in medicine and tips on how to have success as a doctor, and if you want to help me out on YouTube you can always leave me a thumbs up, give me a comment or even subscribe to the channel so that you can find out when the next videos are coming out. So I'll see you again soon!