TB Blood Testing vs. TB Skin Testing

TB Blood Testing

Medically Approved – Dr Salko – 01/31/17 – To be medically assessed again 01/31/18

TB Blood testing and TB skin testing…. The aim of this article is to explain what Tuberculosis is and explain the different methods of testing available.

What is Tuberculosis ?

Tuberculosis (commonly referred to as TB) is a bacterial infection that is passed from one person to another through the air that they share. TB mainly affects the lungs but can affect other parts of the body too. TB is highly contagious and can be transmitted by simply breathing the air of an infected individual who has sneezed or coughed nearby. This bacterial infection can lead to serious health conditions when left untreated.  However, with proper, immediate treatment, TB can be cured.

Persons with TB infection do not feel sick and do not have any symptoms. They are infected with M. tuberculosis, but do not have TB disease. Where as those with TB disease are showing signs of illness.

In 2014, 9,421 cases were reported in the United States to the Centers for Disease Control and Prevention (CDC).

Who should get tested for Tuberculosis?

  • If you have been around someone with TB
  • People who have a weakened immune system
  • Those who have TB symptoms
  • If you had a positive Mantoux test
  • If you have recently visited a country outside of the USA where TB is high risk
  • If you are a healthcare worker, working with high risk individuals
  • Illegal drug users

There are two ways to test for Tuberculosis (TB)…

Tuberculin Skin Test (TST)

A TB skin test is done to see if you have ever been near TB. A small amount of TB proteins are placed under the skin to see if you have a reaction. If you have been exposed to TB you will see a red bump on the testing area.

The limitations of the skin test is that they do not tell you whether you have inactive TB or active TB. Active TB means that you can pass it on to others.

The reason for the skin test is to find those that have TB.

If you know that you have TB you should not have a TB skin test. Also, if you have a rash it can make it harder to give an accurate reading of the results of the test. It is therefore advised not to have a TB skin test.

Once the skin test is completed you must return 2-3 days later and a healthcare worker will check the results.

The other option is Interferon Gamma Release Assay (IGRA), TB Blood Testing

There are currently two of these tests available in the United States:

QFT–GIT or QuantiFERON®–TB Gold In-Tube test and the T–SPOT®.TB test also know as the T–Spot

What is the QFT–GIT or QuantiFERON®–TB Gold?

It is a simple blood test to aid in the diagnosis of the TB virus. It is a modern procedure for the detection of TB as the skin test procedure is now over 100 years old. The test has been approved to help diagnose both TB infection and the TB disease. 

How does the QuantiFERON TB Gold test work ?

TB blood testing explained – A sample is taken at a lab, and tested. The results are then reported to the healthcare provider or your lab management company.

If the results come back positive this means that the person has been infected with TB. To decipher whether the person has the TB disease or the TB infection, additional tests are required.

If the results come back negative, then it is highly unlikely that the person has TB.

The QuantiFERON TB Gold test (TB Blood Testing) is FDA approved.

Blood samples must be processed within 12 hours.

Blood Test vs Skin Test…

If you are going to struggle to go back for a follow up appointment for the TST then the blood test will be best as only one test is required and the results are given electronically.

False positives can occur in a TST if you have had a BCG.

Simple positive or negative results from a blood test

Skin test has increased risk of errors whereas the blood test is in a laboratory setting.

Note – It is not recommended to have both the TST and the TB blood testing.

Resources –





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