Why HBcAg is not detected in Serum?

Last updated on June 11th, 2021

During the lab diagnosis of hepatitis B virus infection, we perform serological tests in which, we can detect antigens; HBsAg, HBeAg, and antibodies; Anti-HBs, Anti-HBc. You might have wondered if there is an antibody in the serum against Hepatitis B core antigen, why we can not detect hepatitis B core antigen (HBcAg) from the serum?  In this blog post, I have collected some information to clarify this issue.

Hepatitis B core antigen (HBcAg) is an intracellular antigen synthesized within infected hepatocytes. Hepatitis B core antigen (HBcAg) are expressed by infected hepatocytes only.

Hepatitis B Core Antigen production and Assembly (source: http://depts.washington.edu)

  Most of the HBcAg that is generated is assembled into the viral core (nucleocapsid). Free HBcAg does not circulate in significant quantity in the blood, but it does circulate as part of the intact hepatitis B virion. So HBcAg is not detected in serum tests but antibodies produced against HBcAg i.e. (anti-HBc) can be detected in the serum throughout the course of HBV infection.

About Acharya Tankeshwar 473 Articles
Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. I am working as an Asst. Professor and Microbiologist at Department of Microbiology and Immunology, Patan Academy of Health Sciences, Nepal. If you want me to write about any posts that you found confusing/difficult, please mention in the comments below.


  1. Thanks, that’s exactly what I needed to know, why we can’t test for Hep B antigen. Your answer makes perfect sense. I will be able to remember this fact forever now.

  2. Yes, since you are so smart and helpful, maybe you can help me with the “window period” of Hepatitis infections. I understand the concept that antibodies will not be detectable until they outnumber the antigens. That makes sense.

    My question is, is this a UNIVERSAL principle, or does it apply only to certain antigen-antibody pairs? If so, why?

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