Recallab › Blog › Hepatitis B serology for NEET PG: reading HBsAg, anti-HBc and anti-HBs

Hepatitis B serology for NEET PG: reading HBsAg, anti-HBc and anti-HBs

MicrobiologyPublished 29 October 2026 · Recallab

Hepatitis B serology is a favourite NEET PG decoder. Three markers do most of the work, and each answers one question: is the virus here now, has this person ever met it, and are they protected?

Three markers, three questions

HBsAg, the surface antigen, means the virus is present now. Anti-HBc, the core antibody, means the person has met the virus at some time; it appears with infection and lasts for life. Anti-HBs, the surface antibody, means immunity, from recovery or from vaccination.

Two refinements finish the decoder. IgM core antibody dates an infection as recent, while IgG core antibody is the long-lasting one. And surface antigen persisting beyond six months defines chronic infection.

The NEET PG hepatitis B decoder

Pattern	HBsAg	Anti-HBc	Anti-HBs
Acute	+	IgM +	−
Window period	−	IgM +	−
Chronic	+ over 6 months	IgG +	−
Recovered	−	IgG +	+
Vaccinated	−	−	+

In the table, + means the marker is present and − means it is absent.

The window period sits between the surface antigen clearing and the surface antibody appearing. Both surface markers are negative then, and IgM core antibody is the key marker that proves the infection.

Try it: say it once before the questions: surface antibody alone means vaccinated; any core antibody means the person has met the virus.

The first marker

Recallab example 1 · the marker blood banks screen for

A timeline is drawn in the figure across the weeks after hepatitis B exposure, with three markers rising in sequence and a blood bank icon marking only one of them. What is that marker?

Look first: find the marker that rises first, before either antibody.

A timeline drawn across twenty-four weeks after exposure to hepatitis B, with three curves rising in sequence, marker 1, marker 2 and marker 3, and a small blood-bank icon placed only above marker 1. Marker 1 rises first, from around week four, and is noted as first identified in a stored serum sample decades ago. Marker 2 rises next and falls away as marker 1 falls. Marker 3 rises last, only after marker 1 has returned to baseline, and stays raised for years. — Recallab question 57894. Three markers rising in sequence, with a blood-bank icon over one.

AHepatitis B surface antigen
BAntibody to surface antigen
CIgM antibody to core antigen
DHepatitis B e antigen

Show the answer and explanation

Answer: A. Hepatitis B surface antigen

A. Hepatitis B surface antigen. It was once called the Australia antigen, after the serum sample it was first isolated from. It rises within weeks of exposure, before either antibody appears, so testing donated blood for it catches an infected donation in the earliest infectious period. Waiting for an antibody would miss donors who are already infectious.

Why the other options lose: antibody to surface antigen (B) rises only once the antigen has cleared, so it would miss every donation still carrying the virus. IgM core antibody (C) is the earliest antibody, but it still rises after the antigen. Hepatitis B e antigen (D) marks active replication; it appears after the surface antigen and is not the screening test.

Recallab question 57894 · Microbiology › Hepatitis Viruses · reference: Jawetz, Melnick & Adelberg's Medical Microbiology

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Acute or chronic

Recallab example 2 · coinfection or superinfection

Two patients with a positive hepatitis D antibody test are drawn in the figure with their hepatitis B marker panels. Patient 2 has a hepatitis D superinfection on top of chronic hepatitis B, while patient 1 has a coinfection. Which marker separates them?

Look first: both have surface antigen; ask which marker tells you how old the hepatitis B is.

Two panel cards side by side, each listing surface antigen, IgM core antibody and hepatitis D antibody with a plus or minus sign. Patient 1 reads plus, plus, plus. Patient 2 reads plus, minus, plus. — Recallab question 56494. Two hepatitis B and D marker panels, side by side.

ASurface antibody
BIgM core antibody
CHepatitis D antibody
DSurface antigen

Show the answer and explanation

Answer: B. IgM core antibody

B. IgM core antibody. It is high-titre in acute hepatitis B and absent or low-titre in a carrier. Patient 1 has a positive IgM core antibody, so the hepatitis B is fresh and the hepatitis D arrived with it: a coinfection. Patient 2 is surface-antigen positive with a negative IgM core antibody, so the hepatitis B is chronic, and hepatitis D added on top is a superinfection. Hepatitis D can only replicate where hepatitis B surface antigen is being made.

Why the other options lose: surface antibody (A) marks recovery or vaccination; it does not date an infection that is still present. Hepatitis D antibody (C) and surface antigen (D) are positive in both patients, so neither separates them.

Recallab question 56494 · Microbiology › Hepatitis Viruses · reference: Jawetz, Melnick & Adelberg's Medical Microbiology

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Reading a whole household

Recallab example 3 · a carrier at home

A man's hepatitis B surface antigen has been positive on two occasions eight months apart, and he lives with four other adults. All five have now been tested. The figure draws each person's marker panel beside an empty column. Who should be vaccinated?

Look first: read each row: antigen means infected, antibody means protected, neither means susceptible.

A table of five household members with columns for surface antigen, surface antibody and an empty vaccinate column. Row one reads plus then minus; row two minus then plus; rows three and four minus then minus; row five minus then plus. A note says member one has been positive on two occasions eight months apart. — Recallab question 59594. Five household marker panels beside an empty vaccination column.

ANobody in the house
BAll four household contacts
CMembers with neither marker
DEverybody in the house

Show the answer and explanation

Answer: C. Members with neither marker

C. Members with neither marker. Surface antigen positive twice, eight months apart, makes the man a chronic carrier, so the household is exposed every day. Surface antigen in a row means that person is already infected, and a vaccine offers them nothing. Surface antibody means that person is already protected. A row with neither marker is a susceptible person living with a carrier, and vaccinating them is what lowers the household's risk.

Why the other options lose: nobody (A) leaves the susceptible members exposed for life. All four contacts (B) would vaccinate two people whose surface antibody already protects them. Everybody (D) adds doses for the infected and the immune that change nobody's risk.

Recallab question 59594 · Microbiology › Hepatitis Viruses · reference: Park's Textbook of Preventive and Social Medicine

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Drawn from questions #57894, #56494, #59594, #50233, #61700, #54624 in the Recallab bank, each with its own verified answer and current-edition reference. Last reviewed 29 October 2026.