How to Identify a Positive Tuberculosis (TB) Skin Test

What Does a Positive TB Skin Test Look Like?

A positive tb skin test result means that your body has been infected with tuberculosis bacteria. Your immune system will fight off the infection and it may take up to two weeks before you feel well again. If you have any symptoms such as fever or cough, they are likely due to other infections and not from tuberculosis. A negative tb test means that there was no evidence of being infected with tuberculosis bacteria in your body.

The tb skin test is used to detect if someone has latent tuberculosis infection. Lymph nodes contain the active form of TB bacteria which can cause disease. When these lymph nodes become infected, they produce antibodies against the active forms of TB bacteria.

These antibodies are then passed along through the blood stream and detected by a tb skin test. A positive tb skin test result indicates that someone has latent tuberculosis infection in their body. Someone with latent tuberculosis infection cannot develop active TB disease because the active strains of TB bacteria are destroyed during the course of treatment. People with latent tuberculosis infection usually do not get sick enough to require medical attention. They might experience some side effects from the medicine prescribed for them, but they will never develop active TB disease.

How Do You Know If You Have a Positive Tb Skin Test Result?

The tb skin test is a small needle prick applied to the inside of your elbow or the back of your shoulder. The skin is then swabbed with a mixture of proteins and TB bacteria. If you have been infected with tuberculosis bacteria, then your lymph nodes will produce antibodies. Antibodies are chemicals that activate the immune system to fight off diseases. A week after receiving the tb skin test, you will be asked to return to learn your results. If the tb skin test is positive, you will see a reaction at the injection site. The skin will likely become red and swollen at the injection site. It may also hurt or itch. You may also have a fever or a cough.

What to Do If You Have a Positive Tuberculosis Skin Test?

If your tb skin test is positive, you should return in two weeks for a follow-up appointment with your physician.

Sources & references used in this article:

Predictive model to identify positive tuberculosis skin test results during contact investigations by WC Bailey, LB Gerald, ME Kimerling, D Redden… – Jama, 2002 –

A three-way comparison of tuberculin skin testing, QuantiFERON-TB gold and T-SPOT. TB in children by TG Connell, N Ritz, GA Paxton, JP Buttery, N Curtis… – PloS one, 2008 –

Monetary versus nonmonetary incentives for TB skin test reading among drug users by CK Malotte, JR Hollingshead, F Rhodes – American journal of preventive …, 1999 – Elsevier

Comparison of two interferon-γ assays and tuberculin skin test for tracing tuberculosis contacts by SM Arend, SFT Thijsen, EMS Leyten… – American journal of …, 2007 –

Interpretation of the tuberculin skin test reaction by pediatric providers by ER Carter, CM Lee – The Pediatric infectious disease journal, 2002 –