Tuberculosis Testing

Industries with especially high risk of TB exposure are the most likely to have testing programs in place for new hires and employees. The most common industries to require TB tests are:

In some industries such as healthcare, testing is required for new employees and each year following. Anyone who may have been exposed or who has symptoms should be tested right away. This is vital for the health of the individual as well as the health of those around them.

A TB screening can be a simple skin test, blood test and/or chest x-rays. Newer types of blood tests are the Oxford T-SPOT and QuantiFERON Gold. A chest x-ray can be used to rule out TB. There are important things to know about each TB test.

TB is caused by Mycobacterium tuberculosis bacteria, and there are two ways to check for it, PPD skin tests and blood tests.

TB/PPD Skin Test

For the past few decades, the PPD test has been the most common tuberculosis screening. PPD stands for purified protein derivative, and this type of screening test can detect a latent TB infection. It is also called a TB skin test, Tuberculin skin test, or Mantoux test.

To check for a TB infection, a health care provider administers a small amount of PPD under the person's skin. A welt forms, which usually goes away in a few hours.

Two to three days after receiving the injection (48-72 hours), the person returns for an evaluation of the injection site, to see if there is a reaction. If there is no swelling, the test is negative, which means that the patient has never been in contact with the Mycobacterium bacteria that causes TB.

When a Series of Two PPD Skin Tests is Necessary

A series of two PPD tests may be needed for a new hire who doesn't have a previously documented TB skin test. It is also recommended that those with positive PPD tests in the past get a series of two PPDs whenever they are tested.

Administering two tests reduces the chance of a false negative. The second test is conducted 7-21 days after the first one is evaluated. Each PPD test requires two visits, so a complete series of the two PPDs takes four visits.

Oxford T-SPOT and QuantiFERON Gold Blood Draws

The T-SPOT®.TB and QuantiFERON-TB Gold Plus (QFT-Plus) are newer TB blood tests. They provide several advantages, such as a single blood draw with no follow-up visit required if the test result is negative. This type of TB blood test is also known as an IGRA (interferon-gamma-release assay). Since the T-SPOT and Quantiferon Gold TB tests only require a single visit, employers prefer them for workers who are deemed less likely to return to the clinic for the follow-up reading.

BCG Vaccine and PPD Skin Tests

The BCG vaccine is widely administered to people born in countries where TB is more prevalent. However, it is not recommended for use in the U.S., as it regularly triggers false positives on PPD tests. Therefore, those who have received the BCG vaccine should be tested for TB with a blood draw.

The T-SPOT or QuantiFERON Gold TB test is also recommended after a negative PPD test if the employee is at high risk for TB (i.e., HIV-positive) or if they are showing signs and symptoms of TB (persistent cough, chest pain, weakness or fatigue, loss of appetite, fever, chills, night sweats). A TB blood test is also recommended after a positive PPD test.

If you receive a positive result from TB skin and blood testing, you have been infected with Mycobacterium tuberculosis, but it does not necessarily mean that you have active TB disease.

A chest X-Ray is indicated if someone receives a positive result on a TB blood test or skin test and is experiencing TB signs or symptoms. Chest X-rays show the condition of the lungs, heart and chest wall, so that a medical expert can make a diagnosis. A chest x-ray can be taken from two viewpoints, frontal or lateral. Lateral and frontal chest X-rays are often done together for a more expanded view of the lungs and chest cavity, especially if the diagnosis is not clear.

In a positive TB test result, a person's chest X-rays will usually show infiltrates, which are spots such as blood or protein, which are denser than air. Infiltrates on a chest x-ray can indicate another disease, such as pneumonia, so it cannot with 100 percent certainty diagnose active TB. However, it is used to rule out TB in cases of positive blood or PPD tests, if the x-ray is clear.

In rare cases where TB is not rules out by a chest X-ray, the person must undergo additional medical care and analysis. There are treatments for TB, which may become necessary, since if left untreated, it can permanently damage the lungs and may be fatal. TB is also extremely contagious, making it a public health concern.

Health Street is your partner in occupational health and employee wellness.