There are two main types of tuberculosis (TB) testing options, a TB screening and a TB test. A TB screening (a blood or skin test) checks to see if you have an immune reaction to TB. This shows if you were exposed to TB in the past, even if you don’t have symptoms.
A tuberculosis sputum test looks for the TB bacteria. Doctors recommend this test for those with symptoms of TB.
What Is Tuberculosis and How Does It Spread?
Tuberculosis is a disease caused by TB bacteria. Someone infected with TB bacteria can spread it to another by coughing, sneezing, singing, or talking in a poorly ventilated area.
People have to breathe in enough of the bacteria to get sick. For this reason, TB spreads between close contacts, rather than between passing strangers.
Most healthy people don’t get sick from TB. Instead, they get what’s called latent TB. Their immune systems fight off the bacteria so that it goes into a dormant state and doesn’t reproduce itself in the body.
People with latent TB don’t get symptoms and don’t spread the germs to others. For this reason, if you were in contact with someone with latent TB, you don’t need to get tested for TB.
But latent TB can turn into active TB in the future. If a health condition or treatment weakens the immune system, the latent TB can begin to multiply. Then, the person develops active TB.
TB can lead to lesions in the lungs that make it difficult to breathe. Without treatment, it can be fatal. Doctors treat TB with antibiotics, taken over months.
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What Are the Symptoms of TB?
Tuberculosis symptoms can show up weeks after contact with a person who has active TB. Symptoms shortly after infection are much more common in young children or in adults with weak immune systems.
In other cases, tuberculosis symptoms won’t show up until years after exposure, usually at a time another health condition weakens the immune system.
People are more likely to get active TB if they have a condition that weakens the immune system, such as HIV, diabetes. Steroids or other immunosuppressive drugs can also make a person vulnerable to active TB disease.
Tuberculosis symptoms include:
- A cough that lasts for more than three weeks, and produces mucus and possibly blood.
- Weight loss.
- Feelings of weakness.
- Loss of appetite.
In rare cases, TB can also spread to other parts of the body, beyond the respiratory system. It can infect the kidney, causing urine in the blood. It can affect the spine, causing back pain. TB can also infect the fluid around the brain, causing headache or confusion.
What Is a TB Screening?
Your health provider may also suggest a tuberculosis screening if you recently traveled from a country with high TB rates. Some workplaces also require TB screening for all employees. Many hospitals require health workers to undergo TB screening upon hire to protect patients who may be especially vulnerable to TB.
A TB screening checks for an immune reaction to TB in someone with no symptoms. TB screening options include a skin test or a blood test.
TB screening skin test
In this TB screening test, a health provider uses a needle to insert a small amount of protein from the TB bacteria under the skin. Because this is not the bacteria itself, it won’t make you sick. If you have already been infected with TB in the past, the skin around the area will react to the protein.
The health provider will ask you to come back sometime between 48 and 72 hours after the injection. Then they will examine the site. The health provider will look for redness and measure the swelling to determine if you’ve been infected with TB.
Skin tests may be falsely positive for people who have received a tuberculosis vaccine in the past.
TB screening blood test
In the blood screening test, a nurse or technician will use a needle and syringe to withdraw a small sample of your blood. This sample then goes to a lab, where a lab technician mixes it with proteins from TB bacteria.
If you have been infected with TB, the blood cells will be ready to fight, so they will release a protein called interferon-gamma (IFN-y). The test is positive if the lab finds the presence of IFN-y in your sample.
Doctors will recommend blood tests for people who have received a tuberculosis vaccine in the past, as they measure a non-vaccine related immune reaction.
What Is a TB Sputum Test?
Unlike a screening, which tests for an immune reaction, this TB testing method tests for the presence of the actual TB bacteria. Doctors use sputum tests for people who have a positive screening test, to find out if they have latent TB or active TB.
People who have symptoms of TB and a high likelihood of having the disease should also get a TB test. This is the case even if they recently had a negative screening test, because the screening tests can have false negative results.
To test for TB, doctors will order a sputum culture. For this test, you cough phlegm (mucus that comes from the lungs) into a cup.
A technician uses special methods to look for TB bacteria in the sample. If your sputum contains TB bacteria, you have active TB. This means that TB is making you sick, and you can spread it to others. If it doesn’t contain TB bacteria, you don’t have active TB but may have latent TB.
What Happens If I Have TB?
If you have latent TB (a positive skin or blood test), it is up to you if you want to receive treatment. You can discuss the pros and cons of treatment with your doctor.
Generally, people at risk of developing a condition that could weaken the immune system should treat latent TB. This way, it won’t one day turn into active TB.
The CDC also recommends treatment of latent TB for health workers. If health workers develop active TB, they could spread it to patients with weak immune systems, who could become very sick.
Latent tuberculosis treatment involves once-a-day antibiotics, taken for three months or longer, depending on the regimen.
If you have active TB, treatment is a must. Active TB requires antibiotic treatment for four months or longer. Your doctor will also monitor you to make sure the drugs are working, and your symptoms are getting better over time.
CDC. Fact sheets: Tuberculin skin testing. Link
CDC. Signs and symptoms of TB. Link
CDC. TB risk factors. Link
CDC. Tuberculosis: vaccines. Link
CDC. TB screening and testing of health care personnel. Link
CDC. Treatment for TB Disease. Link
CDC. Treatment Regimens for Latent TB Infection (LTBI). Link
National Library of Medicine. Sputum culture. Link
Medscape. Tuberculosis (TB) work up. Link
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