Tuberculosis Blood Test vs. Skin Test: The Key Differences

May 18, 2023

Tuberculosis (TB) is a serious health concern around the world. It’s highly infectious and kills 1.6 million people worldwide every year1. Many employers require that new employees and volunteers give proof of a negative test, especially in health care facilities and schools.

Before 2005, your only option for TB testing was the multi-visit skin test. The skin test is where you get a small injection into your arm and wait 48-72 hours to have it visually read by a medical professional. The results are very subjective and can differ based on the person who is reading them.

Now, you have the option of a one-time laboratory blood test with clear positive or negative results sent directly to you with far better accuracy than the skin test.

What is a TB Test?

A TB test helps determine if someone is infected with Mycobacterium tuberculosis, the bacteria that causes tuberculosis. There are two ways to test for TB: 

• The Mantoux TB skin test requires 2-4 visits to a health care professional. They inject a small amount of tuberculin into your skin. You must wait 48 to 72 hours to have the results visually read. If you don’t have it tested within 72 hours, you must be retested. 
• The TB blood test is an interferon-gamma release assay, or IGRA. It is a simple blood test that is processed in a lab with a definite positive or negative result, and only requires one visit. There are two blood tests available: QuantiFERON-TB Gold Plus and T-Spot. 

What are the key differences?

TB blood test:

• Objective results.
• Requires a single blood draw in 1 visit with results reported directly to an EHR system.
• Highly accurate, and unaffected by the Bacillus Calmette-Guerin (BCG) vaccine. 

TB skin:

• Subjective results.
• Requires 2 separate appointments and manual results. 
• Sensitivity of 79% and specificity of 97% with specificity being as low as 59% in BCG-vaccinated patients (high false positive).



Quest TB Blood Test

We make it easy to test for the presence of tuberculosis bacteria with our Tuberculosis Blood Test. Quest offers the QuantiFERON-TB Gold Plus test. No doctor visit required, it’s easy to buy a test online and simple to schedule an appointment at a nearby Quest Diagnostics location. You’ll get your results online and you’ll have the option to discuss your results with an independent physician at no extra cost.

What do my results mean?

The result of your test will determine what your next steps are. A negative test means that you have not been exposed to TB bacteria and no further action is required. A positive test means that you have been exposed to, or infected with, TB bacteria, not that you have the disease. 

If you are positive, you will need a chest x-ray to find out if you have an active (TB disease) or a latent infection. If you have been exposed and you have an active infection, you can spread the disease. If you have a latent infection, you cannot pass it to anyone. Other tests can help determine whether you have a latent TB infection, and it is important to do so because you could develop an active infection, even years later, and become very sick. Both active and latent infections require treatment. 

No doctor visit is required to buy your own lab test at questhealth.com. PWNHealth and its affiliates review your purchase to ensure it is medically appropriate before submitting the test order for processing. PWNHealth also reviews your test results and will contact you directly if they require prompt attention. Included in each purchase is the option to discuss your test results with an independent physician; however, you are also encouraged to speak with your primary healthcare provider. 

References:

1. TB is a Pandemic. Accessed April 28, 2023. https://www.tballiance.org/why-new-tb-drugs/global-pandemic

Sources:

1. Tuberculin Skin Testing Fact Sheet. Accessed April 28, 2023 https://www.cdc.gov/tb/publications/factsheets/testing/skintesting.htm
2. Basic TB Facts. Accessed April 28, 2023. https://www.cdc.gov/tb/topic/basics/default.htm
3. Tuberculosis Blood Test. Accessed April 28, 2023 https://www.questhealth.com/product/tuberculosis-blood-test-36970M.htm