Thread by @natesumMRSA

I'm giving a go at my first #MedEd #Tweetorial!

Let's review a topic I get asked fairly often by residents - Hepatitis B (HBV) serology interpretation.

A thread inspired by a chalk talk in resident clinic yesterday.

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Also an #IDDailyPearl!

There are 3 tests that give you all the information you'll need for most patients: HBV surface antibody (sAb), HBV core antibody (cAb), and HBV surface antigen (sAg).

In general: sAb indicates immunity, cAb exposure, and sAg active infection. More details below!

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First up: vaccinated individuals. They have a (+) sAb from the vaccine but have never been exposed (-cAb) and are not actively infected (-sAg).

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Next: exposed individuals who cleared their infection. ~95% of adults who are exposed will clear their infection (while ~95% of exposed infants will --> chronic infection). They've been exposed (+cAb) but now have natural immunity (+sAb) and aren't infected (-sAg).

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Next: the unlucky individuals who haven't cleared their infection. They've been exposed (+cAb) but did not develop immunity (-sAb) and have ongoing viral replication (+sAg).

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Lastly: the lone core Ab. This requires more work to interpret. If it's an IgM then it could be the early window period of a new infection. Could also be a chronic infection with low-level antigenemia (-sAg) or a cleared infection that never developed a sAb (-sAb).

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The lone core Ab should be followed up with an HBV DNA PCR (a quantitative viral load) to give you more clarity on where this patient falls. If negative, then the patient falls into the "cleared infection" group. If positive then you have your answer.

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Lastly: when to treat. This is easy if Pt is coinfected with HIV or getting immunosuppression. Otherwise, this isn't worth memorizing (IMO), but depends on the sAg, eAg, ALT, and HBV viral load. Figure 1 in the guidelines summarizes this well.

aasldpubs.onlinelibrary.wiley.com/doi/full/10.10…

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@ChrisDJacksonMD @JenniferSpicer4 @VarunPhadke2 @foamid