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Tuberculosis

TB test gone awry?

06/29/2007

Question:

I recently recieved my second tuberculin dose for the TB Skin Test that my new employer requires. However, it would appear that the injection was not subcutaneous as it drew blood at the injection site. What happens now? Will my results in two days be affected- if I have a reaction is there a possiblity of serious fever or am I at risk for getting a false positive? I`d like to know what happens to the tuberculin if it has access to my blood. I would ask my nurse except for this and other reasons her competence is questionable.

Answer:

The Mantoux method is the currently recommended method for placement of the tuberculin skin test. The tuberculin solution is injected intradermally (not subcutaneously) on the volar surface of the forearm, producing a wheal of approximately 6 to 10mm in induration. Occasionally, you can get some bleeding at the injection site and it will not interfere with the reading of the test.

From the question, I am assuming that you received the two-step skin test. So, if your second tuberculin skin test is positive, it may be because of a true "boosted" positive reaction. But, if the skin test was placed incorrectly, too deep or too shallow, the result will not be accurate and can result in a false negative or a false positive reaction.

The quantity of tuberculin injected is small; it causes a localized delayed hypersensitivity reaction. Even if a small amount got into your blood stream, you should not have any major systemic symptoms from that.

What are your options if the second test was placed incorrectly?

  1. You can repeat the skin test. Often time, TB health clinics or employee health clinics have experienced technicians or nurses that place tuberculin skin test frequently.
  2. Another option is getting a new blood test for TB called the QuantiFERON-TB Gold test. It is approved in the United States for the diagnosis of latent TB infection, including people who need to get tested yearly for work. However, this test is not currently available nationwide. You can call your local TB control program and they should be able to tell you if it is available in your area.

For more information:

Go to the Tuberculosis health topic, where you can:

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