True or false: “I had the BCG vaccination so I need to get a chest x-ray instead of the PPD”

False! Employee health workers may say that people who have gotten the BCG vaccination–usually from Asia, Africa, or the Caribbean–do not have reliable PPD readings and therefore need chest x-rays. One magazine article reports: “Current Occupational Safety and Health Administration (OSHA) regulations do not require periodic chest x-rays for a health-care worker who is PPD-positive unless symptoms develop.”

Furthermore, according to Ethnomed:

“Prior vaccination with BCG is not a contraindication to TB skin testing, and the CDC guidelines recommend ignoring BCG status when interpreting skin test results and selecting candidates for latent TB treatment. Although BCG vaccination can turn a skin test positive, reactivity due to BCG vaccination wanes over time. If it has been more than 5 years since vaccination, a positive skin test is more likely due to TB infection than vaccination. Furthermore, the larger the size of the PPD reaction, the less likely it is due to BCG. A recent meta-analysis found that reactive skin tests more than 15 years since vaccination or with more than 15 mm of induration were unlikely to be due to prior BCG vaccination.

Interferon-based blood tests such as the QuantiFERON® -TB Gold avoid the possibility of false-positives occurring from BCG vaccination, since cross-reactivity does not occur.”

Be warned that the Quant Gold may come back as “indeterminate” or “borderline” and then you may be in a bit of a pickle and have to get a chest x-ray anyway.

Questions you should make sure to ask someone who has had a past positive PPD:
1. How long ago was it?
2. Have you ever received the BCG vaccine?
3. Did you ever receive treatment for latent TB? (isoniazid)
4. Have you ever had a chest x-ray previously?



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