Laboratory Testing for Hepatitis B, MMR Titers, and Tuberculosis
Order hepatitis B surface antigen (HBsAg) for hepatitis B screening, IgG antibodies to measles, mumps, and rubella for MMR immunity assessment, and an interferon gamma release assay (IGRA) such as QuantiFERON-TB for quantitative tuberculosis testing.
Hepatitis B Serology
For hepatitis B evaluation, the recommended approach depends on your clinical context 1:
- HBsAg (Hepatitis B Surface Antigen): This is the primary screening test to detect active infection
- Anti-HBc (Hepatitis B Core Antibody): Add this if assessing for past exposure or chronic infection
- Anti-HBs (Hepatitis B Surface Antibody): Order this to assess immunity from vaccination or prior infection
Important caveat: If you're testing someone recently vaccinated for hepatitis B, HBsAg can give false-positive results up to 18 days post-vaccination, so draw blood before vaccinating if possible 1.
The guideline specifically recommends age-appropriate revaccination AND serologic testing for HBsAg when evaluating persons with questionable vaccination records 1. Research shows that 40-50% of individuals may lack adequate hepatitis B protection even after vaccination, particularly those vaccinated at birth versus school age 2.
MMR Titers
Order IgG antibodies to measles, mumps, and rubella separately 1:
- Measles IgG
- Mumps IgG
- Rubella IgG
The ACIP guideline explicitly states that serologic testing for IgG antibodies to measles, mumps, and rubella is the alternative approach to revaccination for persons with questionable vaccination records 1. Modern multiplex bead immunoassays can detect all three simultaneously, reducing sample volume and testing time 3.
Critical pitfall: Research demonstrates that 33% of tested individuals may be susceptible to at least one MMR component, with measles immunity being particularly low at 54-66% in some populations 2, 4. This underscores why testing rather than assuming immunity is important.
Quantitative Tuberculosis Testing
Order an interferon gamma release assay (IGRA), specifically:
- QuantiFERON-TB Gold (QFT-G or QFT-GIT), or
- T-SPOT.TB
The 2010 ACIP guideline on IGRAs provides comprehensive recommendations for their use in detecting Mycobacterium tuberculosis infection 5. IGRAs measure cell-mediated immune response to M. tuberculosis antigens and are the preferred quantitative approach.
Key advantages over tuberculin skin test (TST):
- Single patient visit required
- Results unaffected by prior BCG vaccination
- More specific for M. tuberculosis infection
- Objective laboratory-based results
Important considerations for IGRA interpretation 5:
- Indeterminate results (2-8% of tests): Repeat with a new blood sample if clinical suspicion persists
- Unusual Nil values: If the negative control (Nil) shows IFN-γ >0.7 IU/mL, consider repeating
- Low mitogen response: If mitogen response is <0.5 IU/mL by QFT or <20 spots by T-SPOT, the test may be unreliable
Critical clinical point: Neither IGRA nor TST distinguishes latent TB infection (LTBI) from active tuberculosis. A positive result requires clinical evaluation including chest radiograph and symptom assessment to exclude active disease 5. In persons with symptoms or high risk for progression, a positive IGRA should be taken as evidence of infection, but a negative result does not exclude it 5.
Practical Ordering Summary
Single lab requisition should include:
- Hepatitis B surface antigen (HBsAg)
- Measles IgG antibody
- Mumps IgG antibody
- Rubella IgG antibody
- QuantiFERON-TB Gold or T-SPOT.TB
Consider adding based on clinical context:
- Anti-HBc and anti-HBs if assessing hepatitis B immunity or past exposure
- Varicella IgG if assessing chickenpox immunity (often done alongside MMR)