what's up people in this video i'm going to be teaching you everything that you need to know about hepatitis b serology this is brought to you by dirty medicine i know what you guys are thinking you're thinking dirty you are such a better teacher than the professors at my medical school you're a better teacher than all of these other overpriced crappy resources that i wasted money on in my step one and level one prep how can i give back well thank you so much for asking if you're looking for a way to give back and support my channel financially one subscribe to the channel two share my videos with all of your classmates and on all of your social media networks and three consider clicking the join button to sign up to be a dirty medicine member when you become a dirty medicine member you pay 4.99 a month to support my channel financially and in exchange for your contribution you get the sexy dirty medicine logo which will appear after your username anytime you comment publicly on my channel so if you want to give back and help me on my mission to provide free medical education and improve the quality and the flow of free information on the internet your support is greatly appreciated now in this video we'll be talking about hepatitis b serology and i know that as i just said that you had a nightmare or a flashback about those nasty graphs with all of the different antigens and antibodies and now you're shivering you just vomited under your desk and you're having a panic attack and i know the feeling because honestly i remember what it felt like to learn this it's a beast of a topic and it shows up on practice questions and on usmle and comlex pretty often so in this video i'm going to simplify this beast of a topic teach you everything that you need to know and by the end of this video you will feel confident to answer all of these questions let's start by talking about the normal physiology about hepatitis b because once we have this foundation applying it will be a lot simpler and the first anagen that i want to point out is what you see in red so on the surface of the virus you have the hep b surface antigen now just as a little aside the way that all of these shorthands are written out is you see capital h capital b which stands for hep b you see a little letter in this case s for surface and then ag means antigen so hbsag means hep b surface antigen and this is just the antigen that's on the surface of the virus hence the name now the way that you can think about this surface antigen is that it indicates active infection because if the virus is floating in the body the body can see the surface antigen and therefore there's active infection the next thing we need to talk about is this in this inner or this core component of the virus shown in blue and here we have the hep b core antigen so when you see h b c a g that c stands for core now this is protected in the core or in the capsid of the virus and therefore you can't detect the hep b core antigen you can only detect the antibody to hbc and more on antibodies in just a few slides lastly we have the hep b envelope antigen so in the production of the core antigen the virus also kind of spits out this envelope antigen so bottom line here is that as the virus makes the core antigen it spits out or poops out a little bit of envelope antigen and it's this envelope antigen that signals active replication so if you see the envelope antigen this is not part of the mature virus and therefore this signals active replication and when something's actively replicating it means that there's high transmissibility so i'm sort of going into a preview here about what all of these different antigens mean but let's take a look at this by applying it in an example of an infection so what do you see first when there's an infection of hepatitis b well from the perspective of the body the first thing that the body is going to see is the surface antigen and the envelope antigen i mean think about it if you've got a virus floating in the body the body can see the antigen on the surface of that virus so it shouldn't surprise you that the first thing that we see rise up to a higher concentration is the surface antigen here depicted in red additionally as that virus is replicating and therefore as that virus can be transmitted easily that envelope antigen is being pooped out from the inside of the virus so in addition to the surface antigen which again the body can see the surface of the virus because there's active infection the body can also see the byproduct of viral replication which is the envelope antigen here depicted in green now we haven't really talked about antibodies yet you've got antigens and in response to antigens the body makes antibodies to try to fend off the infection and it's the combination of the antigens coming from the virus and the antibodies coming from the body that creates a specific serologic picture for us that we can look at and test writers can put on usmle and comlex and we can figure out is this acute versus chronic is this replicating and transmissible or are we recovered and are we immune so it's very important that we combine the antigen picture with the antibody picture to figure out the balance between the virus attacking and the body defending and that picture and that combination of serology is a great test question because then we can look at that data and figure out what's going on so after the body looks at the acute infection it sees the surface antigen on the virus it sees the envelope antigen being pooed out of the virus it makes anti-hbc now this is the first time we've mentioned an antibody here and recall that i told you that serology cannot detect the core antigen because it's protected in that core of the virus but what happens is that once a hepatocyte becomes infected it actually can express that core antigen on the surface only after infection once an infected hepatocyte expresses the core antigen on its surface the body can then detect that and in response make anti-hbc so the next thing that you see is anti-hbc and like all antibodies this antibody can either take the form of igm meaning it's an acute or recent infection or igg meaning it's a chronic or long-term infection the next thing that you see is the antibody hbe and i want to pause for a second and take everything off of the slide with the exception of the e antigen and the e antibody and what i'd like to point out to you is that the e antigen or the envelope antigen goes away as the body makes anti hbe and that should make a little bit of sense and the way that you could conceptualize this is that the antibody against the envelope knocks out the envelope antigen so when you're looking at a graph of serology and you're trying to study and make connections here it would be worthwhile to think this way that the antibody takes away the antigen now let's go back to our big picture here so this is where we are so far and i'm gonna restate some of this information to help encode it into your brain so there's an active infection the first thing that the body sees is the surface antigen because it can see the surface of the virus it also sees the envelope antigen because it sees the envelope antigens being pooed out of the virus as the core antigen gets made once a hepatocyte becomes infected the core antigen then goes on the surface of the virus and the first antibody that gets produced in response to that core antigen being on the surface of the virus is the antibody to hbc and that's shown in orange the next antibody that gets produced is the antibody to hbe and you see that as the e antigen goes down the e antibody shows up the last antibody that shows up is the antibody to hbs and again if i were to pause for a second and take everything off the slide with the exception of the surface antigen and surface antibody what you would see is that as the anti-hbs shows up the s antigen goes away so again if you're trying to simplify this and conceptualize here anti-body takes away antigen so the antibody shows up the antigen goes away now here's the full picture and the full timeline of everything that has happened thus far and this is really the complete picture and this is all you need to know you of course need to be able to apply all of this information and infer what's going on with infection immunity and transmissibility but this is the timeline for antigens and antibodies so now for your studying pleasure let's fill out this chart to make sure we fully understand antigens and antibodies and we'll go through them one at a time so we'll start with antigens and then we'll talk after that about antibodies and i have mnemonics for each of these to help you memorize what's going on so for the surface antigen it indicates hepatitis b infection that infection can be either acute or chronic it doesn't matter because the body's looking at the virus whether it's an acute infection or a chronic infection it sees the surface antigen so when it comes to the s antigen s think sick with hepatitis b if you see the s antigen s for sick the person is sick with hepatitis b that sickness can be acute that sickness can be chronic it really doesn't matter when it comes to the envelope antigen or the e antigen remember this tells you replication and transmissibility because the e antigen is technically not a part of the mature virus and therefore if that e if that envelope antigen is being pooped out of the virus it means that the virus is replicating and when any virus is replicating it's highly transmissible so e for easily spread or easily transmissible for the core antigen it's not clinically relevant because even though i'm telling you what's happening with the core antigen we don't detect it with serology so you can just forget about it and wipe it out of your mind so those are the antigens the mnemonics are very simple and incredibly high yield s for sick e for easily spread now let's talk about the antibodies just to make sure we really understand what's going on so anti-hbc tells you that there's either a previous or ongoing infection remember once the hepatocyte gets infected the core antigen goes to the surface of the virus the body sees that and then makes the anti-hbc so if that's igm anti-hbc it tells you that it's an acute infection if it's anti-hbc igg that tells you that it's chronic so when you see c you want to think that the person has come across h or hep b so anti-hbc c for that they've come across hep b either previously or it's ongoing remember that anti-hbe is just the opposite of the e antigen so if the e antigen tells you that the virus is replicating and is easily transmissible then once you have anti hbe now there's low transmissibility so anti hbe means that it's anti spread or not easily transmissible should make sense and then lastly for anti-hbs at this point you have the antibody against the surface antigen which means you have the antibody against active infection which means you finally have immunity now that immunity can either be from natural recovery so the person has gone through the course of the virus and has recovered or that antibody can be due to vaccination so the way to remember that is that anti-s is anti-sick or you're not sick and therefore you're immune so i hope that going through this table was useful to you and that this makes sense i do believe that this is very intuitive but here you have some really clutch mnemonics if you need them now really the last thing that we need to do to put all of this information together so that you are comfortable answering any question that comes up on step one level one or any other exam is to test yourself and the way that this will be presented to you likely on usmle or comlex is they're going to give you a lab print out telling you whether or not different anagens and antibodies are positive or negative and you need to synthesize that information and make a decision about what type of infection or what type of recovery is going on so what i'm going to do now is give you examples and you can test yourself to see if you know what's happening so here's our first example uh hbs antigen is negative anti-hbc is negative and anti-hbs is negative what's going on you can pause the video if you want more time but really what's happening is nothing i mean the person is susceptible they have a negative surface antigen so there's no active infection they have a negative core antibody so they have no previous or ongoing infection and they have a negative surface antibody so there's no immunity so nothing's happening here they don't have the virus they're not immune from the virus they're technically susceptible what about this example the person has a negative surface antigen a positive core antibody and a positive surface antibody what's going on here pause the video if you want more time but this person is immune and they're immune due to natural hep b infection so because their surface antigen is negative they have no active infection but their core antibody is positive which means that they have either a previous or ongoing infection and because their surface antibody is also positive that tells you that there's immunity so the combination of those two antibodies being positive tell you that they're immune due to a natural infection what about this example in this example we've got a negative surface antigen a negative core antibody and a positive surface antibody what's going on here pause the video if you want more time to think about it but in this example the person is immune and they're immune not due to natural infection but they're immune due to immunization so their surface antigen is negative which tells you there's no active infection their core antibody is also negative which tells you that there's no previous infection and no ongoing infection so if you have a negative core antibody but a positive surface antibody because the positive surface antibody tells you that they're immune but they have no anti-hbc that immunity must have been derived from immunization and not because of natural infection so this one is actually very very high yield when you see this combination this is immunity due to immunization what about this example in this example we've got a positive surface antigen a positive core antibody a positive igm core antibody and a negative surface antibody what's going on here well pause the video if you want some more time to think about it but this is just acute infection so the surface antigen is positive which tells you that there's active infection the core antibodies positive which tells you that there's either a previous infection or an ongoing infection and that makes sense because the surface antigens positive you also have a positive core antibody igm subtype which tells you that the infection is acute lastly because the surface antibodies negative there's no immunity so we've got two things here one is active acute infection and two is no immunity so the answer here is acute infection let's wrap up with this final example what's going on here we've got a positive surface antigen a positive core antibody a negative core antibody igm subtype and a negative surface antibody what's going on here pause the video if you want more time to think about it but this is chronic infection so the surface antigen's positive so you know that there's active infection the core antibodies also positive which makes sense and that tells you that there's either a previous or an ongoing infection but because that core igm is negative it's not an acute infection and therefore it's a chronic infection and the surface antibodies negative so there's no immunity so these are the types of examples that you are bound to see on usmle step one complex level one and honestly step two level two step three level three and beyond if you're going into something like internal medicine this is very important information to know it shows up on exams all the time you know it's high yield if you've been doing practice questions so re-watch this video several times if you need to i do believe that i did a very good job of explaining this in a straightforward way that hopefully made sense by first looking at the physiology and then applying some pretty easy mnemonics and examples to hammer this into your brain if this was useful to you please subscribe to the channel share this video on social media and consider clicking that join button to support my mission to provide free medical education financially love you all good luck