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Tuberculosis

Dx TB with Chest X-Rays

04/22/2009

Question:

I recently had the skin TB test done and it was positive; I also had (when I was little) the BCG vaccination. I was told that the BCG vaccination is why the test was positive, and that they needed chest x-rays to be sure. My x-rays showed a small (+-.5mm) calcification, I was told. They told me that it wasn`t TB. My question is, could the early vaccine have been the reason for that calcification, or was it caused by a concrete past/present TB infection?

Answer:

The BCG vaccine is not the reason for the calcification on your CXR and is unlikely to be the cause of your positive tuberculin skin test (TST). It is true that the BCG vaccine can cause a false positive TST; this is more likely if your BCG vaccine was recent (within the last 10 years).

The small calcification on your CXR is likely a calcified granuloma of the lungs. Granulomas are localized noncancerous nodular inflammation areas of tissue and can be found in a variety of organs including the lungs. Granulomas of the lungs can be caused by infectious organisms such as tuberculosis or fungal infections, but they can also be caused by non-infectious medical conditions and chemical and physical irritants. Because it can take years for calcium to be deposited in a granuloma, a calcified granuloma is likely one that has been there for some time and without a biopsy (tissue sampling) of the lung tissue, the exact cause of the granuloma is unknown.

Calcified granulomas of the lung from TB are usually found incidentally on a chest x-ray performed for other reasons. The individual may have been infected with TB years ago (breathed in the TB bacteria and became infected). The body was able to fight the bacteria to stop them from growing. The bacteria became inactive (latent), but they remained alive in the body in a dormant state and can later become active. This is called latent TB infection. People with latent TB infection have no symptoms, do not feel sick, cannot spread TB to others, and usually have a positive TST or TB blood test.

The current recommendation by the Centers for Disease Control and Prevention (CDC) is to disregard the history of BCG vaccine when interpreting the TST result. So, if your skin test is positive and your CXR is negative, you are diagnosed with latent TB infection. Anyone with a history of exposure to someone with active TB disease or has been diagnosed with latent TB infection should see a doctor to be evaluated for latent TB infection treatment.

There are new blood tests called interferon gamma release assays that can also be used like the TST to find out if you are infected with the TB bacteria or not (The TSpotĀ® TB Test and the QuantiFERON-TBĀ® Test.) These blood tests are NOT affected by previous history of BCG vaccine. Because this test is new, it may not be available in all health departments or hospital laboratories near you.

For more information:

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Response by:

Shu-Hua   Wang, MD, MPH&TM Shu-Hua Wang, MD, MPH&TM
Clinical Assistant Professor of Infectious Diseases
Clinical Assistant Professor of The Division of Epidemiology
College of Medicine
The Ohio State University

Larry S Schlesinger, MD Larry S Schlesinger, MD
Professor:
Molecular Virology, Immunology and Medical Genetics
Microbiology Administration
Environmental Health Sciences
College of Medicine
The Ohio State University