Tuberculosis (TB) Testing

Tuberculosis (TB) is a highly contagious disease that damages the lungs. TB Tests are required for many jobs to ensure that workers are free of tuberculosis. PPD skin tests and TB blood tests are available to diagnose active infections. Each testing method has its pros and cons. Find out which TB Test is right for your employees.

Tuberculosis, known as TB, is a disease that damages your lungs. TB is transmitted from person to person through the air when an infected person coughs, sneezes, or talks. Because it’s known as an airborne disease, it’s important for you as an employer to make sure your workers undergo regular tuberculosis testing. If left untreated, TB could be fatal. Keep reading to find out which industries may be affected by TB and what TB tests are available.

What Industries Require Tuberculosis Tests?

Industries that may be at high exposure risk for TB are most likely to require testing. Here are some of the most common industries that require TB tests:

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Healthcare
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Correctional facilities
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Education
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Nursing homes
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Caseworkers
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Any other industries that work with large populations.

For some of these industries like healthcare, testing is to be done upon hire and then every year after that. It should also be done for anyone who was possibly exposed to TB or is showing signs and symptoms.

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What are the different types of TB tests?

Getting tested for TB can be as simple as a skin test, blood test, and/or chest x-rays.

TB is caused by bacteria called Mycobacterium tuberculosis and there are two ways to check for the presence of this bacteria, skin tests and blood tests.

TB/PPD skin test

The most common TB test over the past few decades has been the PPD skin test.  PPD stands for purified protein derivative. Other names for this test are TB skin test, Tuberculin skin test, and Mantoux test.

A TB skin test is administered by a healthcare provider who administers a small amount of PPD under the patient’s skin. This causes a welt to form that usually goes away within a few hours.

After 48-72 hours of receiving the injection, the patient must return to the healthcare provider, who will evaluate the injection site checking for a reaction. If the test is negative, the injection site should have no swelling. This means the patient has never come into contact with the Mycobacterium bacteria that causes Tuberculosis.

Series of Two PPD skin tests

There are situations in which a series of two PPD skin tests may be necessary. For example, for new hires without a previously documented TB skin test should get two PPD tests. Similarly, those who have had positive reactions to PPD tests in the past are recommended to get a series of two PPDs each time they are re-evaluated.

By administering two tests, the likelihood of a false negative is reduced. The second test is generally given 7-21 days after the first test is administered and read. Note that each PPD does require two visits, so a series of two PPDs requires four visits.

Oxford T-SPOT and QuantiFERON Gold blood draws

The T-SPOT®.TB blood draw as well as the QuantiFERON-TB Gold Plus (QFT-Plus) are newer tests for TB that provide several advantages. These tests require a single blood draw and no follow-up visit for negative results. This type of TB blood test is known as interferon-gamma-release assay (IGRA). Because the T-SPOT and Quantiferon Gold TB blood tests only require a single visit, they are the preferred method for TB testing for those employees who are deemed to be less likely to return to the clinic to get their skin test read.

BCG Vaccine

The BCG vaccine, which is widely administered to people born in certain countries where TB is more prevalent than in the United States, often triggers false positives on a PPD skin test for a lifetime. Therefore, testing for TB via blood draw is the strongly recommended method of TB testing for anyone who has received the BCG vaccine.

The T-SPOT blood draw or QuantiFERON Gold TB Test is also recommended after a negative PPD if the employee is known to be at high risk for TB (such as an HIV-positive employee), or if the employee is showing signs and symptoms of TB. It’s also recommended after a positive TB skin test.

A positive result from TB skin and blood testing means that you have been infected with Mycobacterium tuberculosis and does not mean you have active TB.

Chest X-ray

Anyone who gets a positive result on a TB skin or blood test or is experiencing the signs or symptoms of Tuberculosis needs a chest X-ray. Chest X-rays can give medical providers a better look into the chest to see the lungs, heart and chest wall.

Chest X-rays can be taken from a frontal or lateral viewpoint. Lateral chest x-rays are typically done in addition to frontal X-rays to get a better, overall view of the lungs and chest cavity, especially in cases where the diagnosis is questionable.

In cases of a positive TB test, chest X-rays will typically show infiltrates, meaning that they’ll show spots that are denser than air (such as blood or protein).

Since there are other illnesses that appear as infiltrates on a chest x-ray (such as pneumonia), it cannot diagnose active TB, but rather it is used to rule out TB after a positive skin or blood test, if the chest x-ray is clear.

In the rare case that TB cannot be ruled out by a chest X-ray, additional medical care and analysis is absolutely required. There is a treatment for tuberculosis, but left untreated, it can damage the lungs and become fatal. It’s also highly contagious.

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Citations

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“Tuberculosis.” MedlinePlus, U.S. National Library of Medicine, https://medlineplus.gov/tuberculosis.html
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“PPD Skin Test.” MedlinePlus, U.S. National Library of Medicine, https://medlineplus.gov/ency/article/003839.htm
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“How is two-step tuberculin skin testing done?” Curry International Tuberculosis Center, McHenry County Illinois, https://www.mchenrycountyil.gov/home/showdocument?id=33604
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“The T-Spot .TB Test.” Oxford Diagnostic Laboratories, http://www.oxforddiagnosticlabs.com/products-and-services/the-t-spot-tb-test/
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“Interferon-Gamma Release Assays (IGRAs) – Blood Tests for TB Infection.” Fact Sheets, Centers for Disease Control and Prevention (CDC), https://www.cdc.gov/tb/publications/factsheets/testing/igra.htm
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“TB 101 for Health Care Workers, Lesson 4: Diagnosis of TB Disease – Chest X-Ray.” Centers for Disease Control and Prevention (CDC), https://www.cdc.gov/tb/webcourses/tb101/page3263.html
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“Diagnosing Latent TB Infection & Disease.” Centers for Disease Control and Prevention (CDC), https://www.cdc.gov/tb/topic/testing/diagnosingltbi.htm