What test is used to check for hepatitis A immunity after Twinrix (hepatitis A and hepatitis B vaccine) vaccination?

Testing for Hepatitis A Immunity After Twinrix Vaccination

To test for hepatitis A immunity after Twinrix vaccination, a total anti-HAV antibody test should be used, with a positive result by standard commercial assay indicating protection. 1

Understanding Hepatitis A Antibody Testing

• After Twinrix vaccination, antibody concentrations achieved are 10-100 fold lower than those produced after natural infection and may be below the detection limit of some commercial assays 1
• Standard commercial immunoassays typically have a lower detection limit of approximately 100 mIU/mL, while more sensitive assays used in research settings can detect levels as low as 10 mIU/mL 1
• Anti-HAV antibody concentrations are measured in comparison with a World Health Organization reference immunoglobulin reagent and expressed as milli-International Units per milliliter (mIU/mL) 1

Interpretation of Results

• A positive anti-HAV result by a standard commercial assay definitively indicates protection against hepatitis A 1
• However, vaccinated individuals who test negative by standard assays might still have protective levels of antibody that are below the detection threshold 1
• Clinical studies have used different thresholds to define protective antibody response:
  • HAVRIX studies used levels >20 mIU/mL or >33 mIU/mL (in more recent studies) as measured with modified enzyme immunoassays 1
  • VAQTA studies used levels >10 mIU/mL as measured with a modified radioimmunoassay 1

Timing of Testing

• If testing is deemed necessary, it should be performed 1-2 months after completing the full vaccination series 1
• For Twinrix, this would be 1-2 months after the third dose (given at 0,1, and 6 months) 1

Is Testing Necessary?

• Routine testing for hepatitis A immunity after vaccination is generally not recommended due to:
  • High seroconversion rates (97-100% in adults after completing the series) 1
  • The insensitivity of standard commercial assays to detect vaccine-induced immunity 1
  • Long-term persistence of immunity (studies show protection lasting at least 15 years) 2

Special Considerations

• Testing might be considered for immunocompromised individuals or those with chronic liver disease, who may have lower seroconversion rates 1
• If testing is performed and results are negative by standard assay, this does not necessarily indicate lack of protection 1
• Antibody levels after vaccination with Twinrix are comparable to those achieved with single-antigen vaccines administered separately 1

Common Pitfalls

• Using insensitive assays that may miss protective antibody levels induced by vaccination 1
• Misinterpreting a negative test result as indicating lack of protection when the individual may still have protective levels below the assay's detection threshold 1
• Testing too soon after vaccination before peak antibody levels have developed 1
• Unnecessary testing in immunocompetent individuals who have completed the full vaccination series 1

Remember that Twinrix provides dual protection against both hepatitis A and B. While testing for hepatitis A immunity is generally not recommended after vaccination, testing for hepatitis B immunity (anti-HBs ≥10 mIU/mL) may be indicated in certain high-risk groups 1.