Conversion to Positive TB Test Requires Follow-up

Q:I am a completely healthy 32-year-old teacher and have no medical problems. Two years ago, my TB test (PPD) done for routine employee screening became positive. I had a chest X-ray completed at that time which was normal and I certainly do not know of any tuberculosis exposures.

I recently discussed this with my doctor who told me I needed to take medication to treat me for tuberculosis. Is this really necessary?

A:Sorry, but yes. The PPD (purified protein derivative) tuberculin skin test is done to check for tuberculosis infection. It is a small shot given under the skin by your health care provider. Two days after the shot, you return to have the test read. A trained professional will look for swelling, or in-duration, of skin at the site of the injection. The amount of in-duration indicates whether the test is positive or negative.

There are different levels of “positive” depending on your risk factors to develop tuberculosis. If you have no prior exposures to TB and have never received the BCG vaccine for tuberculosis ( which is rarely used in the US but can result in a positive TB test – what does it look like ), you should not react to the PPD test and your test should be read as negative.

The American Thoracic Society and the Centers for Disease Control both recommend testing for tuberculosis in high-risk people only. As in your case, employee requirements often mandate that even those considered low-risk have PPD tests for tuberculosis.

While you seem to be low-risk, you were tested and it was positive. The American Thoracic Society states that “a decision to TB test is a decision to treat.” We can not just ignore your positive test results, especially because your test recently converted to positive. That is why treatment is recommended.

Since your PPD test is positive but your chest X-ray is normal, we have to assume that somewhere, sometime, you were exposed to TB and you could exhibit symptoms and spread the infection at some point in your life. This is called “latent tuberculosis,” and it requires treatment.

Treatment usually consists of a drug called isoniazid that you would be required to take for 6-12 months. This is certainly nothing that anyone is eager to do. Still, it is very important for your personal health, as well as for public health reasons, that you seek treatment, comply with the regimen exactly as prescribed, finish the entire course, and follow up regularly while undergoing treatment to monitor any side effects.

Deidre L. Faust, MD, is a Staff Physician (Internal Medicine) at the Medical College of Wisconsin’s Plank Road Clinic. Her column appears in the Milwaukee Journal-Sentinel.