Common Ailments

Positive TB Skin Test Information

Abnormal TB Skin Test

What does it mean?

The tuberculosis skin test is designed to determine if you have come in contact with the tuberculosis bacteria. Tuberculosis is generally transmitted from person to person in the air. It is a bacteria. If a human inhales the tuberculosis bacteria three things can happen:

1. The bacteria spreads in the lungs becoming an infection called pneumonia. People with this problem have a cough and fever. A chest x-ray will help determine if a person has this disease.
2. The tuberculosis bacteria is destroyed by our immune system. A chest x-ray will be normal in this situation
3. The tuberculosis bacteria "walled off" or "hibernates" and becomes a small seed or stone in the lung. This is called a tubercule. The tubercule may open up and spread into the lung and other parts of the body several months or years later. This is also called "latent tuberculosis." A chest x-ray will also be normal in this situation because the tubercule is too small to see on an x-ray.

The TB skin test can not determine which one of these three things has happened to you. It only determines that you have been exposed to tuberculosis.

What is the next step?

If the TB skin test is abnormal you will need to determine which one of these three things has happened. A chest Xray will be done first. If the X ray is normal, then there is no pneumonia (situation #1). However, the bacteria still could be living as a tubercle in the lung (situation #3).

If the Xray is normal there are several options:

A. Assume that the bacteria tubercle is living in the lung and take antibiotics to destroy the bacteria.
B. Repeat X-rays every year to determine if the bacteria is growing.
C. A new blood test is available that can tell if the bacteria has been destroyed or if it is living in the lung.

Option C is the most straightforward option and offers the most definitive answers. You and your doctor can determine which option is best for you.

Written by P. Davis, M.D. 07/19/2010