Blood Test for Tuberculosis Diagnosis: Everything You Need to Know

Tuberculosis (TB) is a serious infectious disease that primarily affects the lungs. Accurate and timely diagnosis is crucial for controlling TB and preventing its spread. A Blood Test For Tuberculosis Diagnosis, also known as an interferon-gamma release assay (IGRA), is a modern and effective tool used to detect TB infection. This article provides a comprehensive overview of TB blood tests, helping you understand their purpose, procedure, and significance in diagnosing TB.

What is a TB Blood Test?

A TB blood test is a diagnostic test that uses a blood sample to determine if you have been infected with Mycobacterium tuberculosis, the bacteria that causes TB. These tests, scientifically known as interferon-gamma release assays (IGRAs), work by measuring your immune system’s response to TB bacteria.

Specifically, the test involves mixing a small sample of your blood with TB proteins. If you have been infected with TB bacteria, even if it’s a latent infection, your immune cells will release interferon-gamma in response to these proteins. The test then measures the amount of interferon-gamma to indicate the likelihood of TB infection.

There are two main types of TB blood tests approved for use in the United States:

QuantiFERON®-TB Gold Plus (QFT-Plus): This is an IGRA blood test that is widely used.
T-SPOT®.TB test (T-Spot): Another type of IGRA blood test that offers a different approach to measuring the immune response.

Both tests are highly reliable and offer advantages over the traditional TB skin test, particularly in certain populations.

Who Should Get a TB Blood Test?

While anyone can receive a TB blood test, it is particularly recommended for certain groups, including:

Individuals who have received the BCG vaccine: The Bacille Calmette-Guérin (BCG) vaccine is a TB vaccine used in many countries where TB is common, but not widely used in the United States. BCG can cause a false-positive result on the traditional TB skin test. TB blood tests are not affected by prior BCG vaccination, making them the preferred testing method for people who have received the BCG vaccine.
People who may not return for a TB skin test reading: The TB skin test requires a return visit to a healthcare provider 48 to 72 hours after administration to have the results read. For individuals who may find it difficult to return for a second appointment, a TB blood test is a convenient alternative as it only requires a single blood draw.

TB blood tests are considered safe during pregnancy. However, it’s important to note that TB blood tests have not been specifically evaluated for diagnosing latent TB infection in pregnant women. Consult with your healthcare provider to determine the most appropriate testing method for your situation.

How to Get Tested for TB

Getting tested for TB is a straightforward process. You can get a TB blood test at various locations, including:

Your healthcare provider’s office: Routine check-ups or specific concerns about TB are good opportunities to discuss testing with your doctor.
Local health departments: Public health departments often offer TB testing services, sometimes at low or no cost.

Your healthcare provider will determine the most suitable TB test for you based on your individual risk factors and circumstances. The costs associated with TB testing are generally covered by both public and private health insurance plans.

For finding a testing location near you, contacting your state or local TB program is a helpful step. They can provide information on available testing services in your area.

State TB Programs

Understanding Your TB Blood Test Results

Interpreting your TB blood test results is crucial for understanding your TB status and next steps.

Positive TB Blood Test Result

A positive blood test result indicates that you have been infected with TB bacteria. It means TB germs are present in your body. It is important to understand that a positive blood test only indicates infection and does not differentiate between latent TB infection (inactive TB) and active TB disease. Further tests are necessary to determine if you have active TB disease.

Keep a record of your positive result: Once you have a positive TB blood test or TB skin test, future tests may also be positive, even after successful treatment for either latent TB infection or active TB disease. It is advisable to obtain a written record of your positive result from your healthcare provider. This documentation will be beneficial if you are required to undergo TB testing again in the future.

Negative TB Blood Test Result

A negative blood test result for TB infection suggests that TB infection is unlikely. However, it does not completely rule out TB, especially if you have recently been exposed to TB or have symptoms of TB disease. Your healthcare provider may recommend further investigations, particularly if there is a high suspicion of TB based on your health status or exposure history.

What Happens After You Get Your Results?

Following your TB blood test results, appropriate steps will be taken based on whether the result is positive or negative.

If you have a positive TB blood test result, it means you have TB germs in your body and further evaluation is needed. Your healthcare provider will conduct additional tests to determine if you have:

Latent TB Infection (Inactive TB): In this condition, TB bacteria are present in the body but are inactive and do not cause symptoms or spread to others. Treatment is usually recommended to prevent latent TB infection from progressing to active TB disease.
Active TB Disease: In this condition, TB bacteria are active, multiplying, and causing illness. Active TB disease can be contagious and requires immediate treatment to cure the disease and prevent transmission.

These further tests may include a chest X-ray and a sputum test (testing the phlegm you cough up). Your healthcare provider will discuss your diagnosis with you and recommend the appropriate treatment plan based on whether you have latent TB infection or active TB disease.

Keep Reading: Diagnosing Tuberculosis