Hep B viral markers

Question 1

What first 2 investigations are done when screening for hepatitis B (after LFTs etc)?

Answer 1

• HBsAg (surface antigen): represents active infection
• HBcAb (core antibody): differentiates between acute/chronic/past infection

Question 2

How to interpret HBcAb result?

Answer 2

• High IgM means acute infection; low/negative IgM titre=chronic infection
• High IgG means past infection (if HBsAg is negative, if positive means chronic infection)

Question 3

What other investigations can be done if HBsAg and HBcAb are positive?

Answer 3

• HBV DNA (hep B DNA): can count viral load (thus inferring infectivity)
• HBeAg (hep B envelope antigen): raised during active replication (acute phase) and directly correlated with infectivity (high levels = very infectious)

Question 4

What is HBsAb and what does it indicate?

Answer 4

• Hep B surface antibody
• Positive if an immune response to HBsAg has been mounted
• Therefore indicates vaccination or previous infection (interpret with other results)

Question 5

An ‘equivocal’ HBsAg result can come back in what instance?

Answer 5

• Recent Hep B vaccination
• Will also have positive HBsAb