Occupational Health Screening: Blood Tests for Chickenpox Immunity and TB Assessment
Order varicella-zoster virus (VZV) IgG antibody testing and an interferon-gamma release assay (IGRA) for this patient's occupational health screening.
Varicella (Chickenpox) Immunity Testing
Order VZV-specific IgG antibody testing to document immunity for workplace requirements, even with a positive childhood chickenpox history 1.
Key Testing Considerations:
A positive history of chickenpox is generally reliable for immunity, but serologic confirmation is often required by employers for healthcare and certain other occupational settings 1
Use sensitive antibody assays such as fluorescent antibody to membrane antigen (FAMA) or latex agglutination if standard ELISA testing is negative, as commercial ELISA assays may miss low-titer vaccine-induced or remote natural infection antibodies 2
If initial testing is negative despite positive history, consider more sensitive assays before proceeding to vaccination, as some individuals maintain cell-mediated immunity without detectable antibodies by standard commercial ELISA 2
Tuberculosis Screening with IGRA
Order an IGRA (QuantiFERON-TB Gold or T-SPOT.TB) as the preferred test for occupational TB screening in this adult patient 1.
Rationale for IGRA Selection:
IGRAs are recommended over tuberculin skin tests (TST) for adults in occupational screening because they require only a single visit, eliminate the need for return appointments for reading, and have higher specificity 1
IGRAs are particularly advantageous in populations with historically low rates of return for TST reading and in settings where a single-visit test improves completion rates 3
For adults aged ≥5 years, IGRA performance is well-established with sensitivity and specificity comparable to or better than TST, making it the preferred choice for routine occupational screening 1
Important Testing Caveats:
If the patient has a history of BCG vaccination, IGRA is strongly preferred as it will not produce false-positive results from BCG, unlike TST which has only 85% specificity in BCG-vaccinated populations compared to 99% for IGRA 4
A positive IGRA indicates M. tuberculosis infection (either latent or active) and cannot be attributed to BCG vaccination; it requires clinical evaluation to exclude active TB disease before considering latent TB treatment 4, 3
A negative baseline IGRA does not exclude recent exposure; if there is known TB contact within the past 8-10 weeks, repeat testing should be performed 8-10 weeks after the last exposure 3
Request quantitative IGRA results rather than just positive/negative, as values near the cutoff are less reliable and quantitative reporting allows better interpretation of borderline or repeat results 1
Post-Test Management:
If IGRA is positive, clinical evaluation including symptom assessment and chest radiography is mandatory to exclude active TB disease before any consideration of latent TB treatment 3
If IGRA is negative and there is no recent TB exposure, no further TB testing is needed for baseline occupational clearance 1, 3
IGRA testing is associated with significantly higher treatment completion rates (55% vs 42% for TST) if latent TB infection is diagnosed and treatment is indicated, supporting its use as the initial diagnostic test 5