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Taking a tuberculosis test is your first step to securing effective treatment for the infection. After the COVID pandemic, much attention was paid to other pulmonary infections like tuberculosis, especially since cases have started to rise in 2022. In this guide, we outline how TB develops, the testing options, and its prevalence in the US.
Tuberculosis, or simply TB, is a bacterial infection passed from one person to another through the air they share. It primarily affects the lungs but can also affect other body parts, such as the bones, joints, kidneys, brain, lymph nodes, abdominal area, and spine.
Tuberculosis is highly contagious and can be transmitted by simply breathing the air of an infected individual who has sneezed or coughed nearby. The primary bacteria responsible for the disease is called Mycobacterium tuberculosis(1).
When left untreated, tuberculosis can lead to serious health conditions. However, with proper, immediate treatment, TB can be cured.
Read more: 7 Things You Should Do If You’re Diagnosed With Pulmonary Tuberculosis
Active TB is when the bacteria quickly multiply and travel throughout various body organs.
A person with this illness is contagious and can pass TB to others through coughing, sneezing, and breathing in the close vicinity of others.
On the other hand, a person with a latent TB infection is not contagious, does not feel sick or have any symptoms, and, in some cases, isn’t aware of their condition.
However, latent TB could develop into an active disease and, therefore, should be monitored. People with a weakened immune system are at increased risk of latent TB progressing to active TB.
There are two types of blood tests for tuberculosis. Both follow unique lab protocols and measure different biomarkers for the disease.
The QuantiFERON®–TB Gold or QFT-Gold is a simple blood test to diagnose TB. It is a more modern procedure for detecting past and present TB infections, as the skin test procedure is over 100 years old.
A blood sample is required to perform the test. In general, it evaluates the reaction of the white blood cells to TB antigens in a carefully set testing environment.
A positive tuberculosis test following this protocol will show high levels of a protein released by the white blood cells called interferon-gamma (IFN-gamma). Typically, this exceeds 0.35 IU/mL (milliliter per international unit). Otherwise, it’s deemed normal and rules out TB.
However, keep in mind that this tuberculosis blood test does not necessarily indicate an ongoing TB infection. That is to say, the positive test result can be due to latent tuberculosis. Hence, the next step is to undergo testing for the specific type of TB.
T–SPOT® TB test, also known as the T–Spot, is another blood test that indirectly detects TB infection. It’s different from the QuantiFERON®-TB Gold blood test in that it measures how many T cells producing interferon-gamma there are after exposing the white blood cells to TB antigens.
T-Spot is regarded as more sensitive than QFT-Gold, making it more suitable for individuals with compromised immune systems. However, It can be more expensive and requires a longer turnaround time.
A TB skin test is performed to determine if you’ve been exposed to tuberculosis. TB proteins are injected into the skin to trigger an immune reaction, which will be confirmed by the appearance of red bumps.
The limitation of the skin test is that it doesn’t tell you whether you have latent or active TB but rather if you have TB regardless of type. Once the skin test is completed, you must return 2-3 days later, and a healthcare worker will check the results.
In a TB sputum test, you will provide a sample of your mucus. This will be analyzed in the lab for culture and bacterial identification through smear microscopy.
The mere presence of Mycobacterium tuberculosis can confirm TB infection. However, it does not verify if the disease is active or latent. Hence, your healthcare provider will turn to the sputum culture. A positive result for the culture indicates active TB.
According to the Centers for Disease Control and Prevention (CDC), an estimated 13 million people in the US have latent TB infection. Meanwhile, in 2022, the reported number of TB cases was 8,331(2).
Tuberculosis is less common than other pulmonary diseases like bacterial or viral pneumonia. However, cases gradually increase by 2022. That’s not to say that TB is on its way to becoming the new endemic disease. At the very least, it indicates that general immunity should be strengthened to eradicate tuberculosis completely.
X-rays may help diagnose tuberculosis, but they are not a definitive diagnostic measure on their own. During an X-ray procedure, an individual with an active TB infection might show inflammation, fluid buildup, and lung cavities. However, this typically occurs in a much later stage. Hence, an X-ray may not detect the infection when testing for tuberculosis at its onset.
While latent tuberculosis shows no symptoms, an active TB infection may cause a cough with mucus (even blood-stained mucus) lasting over three weeks. In addition, you’ll also feel chest pain, fatigue, appetite and sudden weight loss, malaise (feeling unwell), night sweats, and high fever.
Silent tuberculosis can be associated with two conditions involving the infection. Although it’s not necessarily a clinical term, the word silent may refer to latent tuberculosis, a form of the disease with no symptoms and can’t be contagious to others. On the other hand, it can also refer to the early stage of TB, wherein the symptoms are typically mild and similar to other respiratory diseases like the common flu. As a result, it is easily overlooked as tuberculosis.
For decades, tuberculosis cases declined. However, the trend has been overturned, making it imperative to understand how it is diagnosed and who is at risk. If you have been exposed to someone with TB, consult a doctor even if symptoms are not observed. Early detection warrants proper testing and treatment.
1 Adigun R, Singh R. Tuberculosis. 2023 Jul 11. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan–. PMID: 28722945.
2 Centers for Disease Control and Prevention (2023, November 15). Tuberculosis Data and Statistics. CDC. Retrieved March 10, 2024, from https://www.cdc.gov/tb/statistics/def
