TB Testing: Who Needs It, What a Positive Result Means
Tuberculosis detection starts with a simple test
Tuberculosis detection starts with a simple test
Tuberculosis (TB) is contagious bacterial infection that usually affects the lungs though it may involve other parts like the spine, kidneys or brain.
It spreads when people with active TB cough, sneeze or speak. These germs can stay in the air for several hours, depending on the environment. The bacteria that causes TB can stay in the body for years without showing symptoms.
While it is less common in the United States, TB remains a serious concern because it spreads easily and can become contagious if inactive infections are left untreated.
“In some cases, the immune system fights the infection. Instead of becoming sick with TB, these people have what is known as latent TB infection,” says Zhaoyi Qin, MD, an internal medicine physician at Scripps Clinic Torrey Pines. “This means they have the bacteria in their bodies, but do not have active TB.”
People with inactive TB do not feel sick and cannot spread the disease. However, if latent TB is not treated, it can turn into active TB, which is contagious. This can happen without warning, so it is important to get tested for tuberculosis and learn if you are at risk of infecting others.
How common is tuberculosis?
After almost 30 years of steady decline in TB cases, the numbers started to rise again in 2021. There was a sharp drop in 2020. This upward trend has continued, likely influenced by pandemic-related health care disruptions, increased international travel and migration and localized outbreaks in several states.
The U.S. recorded 9,633 tuberculosis cases in 2023. Early data from 2024 shows that number increased to 10,347 — an 8% rise year over year.
These recent developments highlight how important it is to test and treat latent TB infections early to prevent future spread.
Who should get tested?
Anyone can get tuberculosis, but some people are at higher risk. Testing is recommended if you:
- Have a persistent cough, chest pain, or cough up blood or phlegm
- Spent time near someone diagnosed with TB
- Have a weakened immune system (HIV, cancer, diabetes or are taking immune-suppressing medications)
- Live or have lived in large group settings like homeless shelters, prisons or jails or long-term care facilities
- Inject illegal drugs
- Were born in or travel to countries where TB is common, including countries in Asia, Africa and Latin America
Children, especially those under five, are more likely to get TB disease if they are infected with TB germs.
“Testing is recommended, if not required, before starting a new job, transferring to a different school or volunteering,” says Dr. Qin. “Testing is especially important in schools, health care environments and other places where the risk of TB is increased because of close contact between people who may be ill or have weak immune systems.”
How is TB testing done?
Two types of tests are used to detect tuberculosis in the body:
TB skin test: The TB skin test involves injecting a small amount of fluid under the skin of your forearm. The injection site is checked within 48-72 hours by a health care provider. Swelling or bumps may indicate TB infection.
If you’ve had a TB vaccine, such as the BCG vaccination, let your provider know. The vaccine can cause skin test results to appear falsely positive. In such cases, a blood test may be preferred.
The TB vaccine is not widely used in the U.S. However, it is commonly given to infants and small children in countries where TB is more common.
TB blood test: A TB blood test, known as an interferon-gamma release assay (IGRA), checks how your immune system responds. A small amount of your blood is mixed with TB proteins. You only need one visit to a health care provider. This test is not affected by prior BCG vaccination, which can cause false positives in skin tests.
What if my TB test is positive?
A positive TB test indicates the presence of TB bacteria. However, it does not tell you whether you have latent TB or active TB disease. Your doctor will order additional tests, such as a chest X-ray, to determine the next steps.
If you have active TB: You’ll need to take TB medicine, usually a combination of antibiotics, for four to nine months.
If you have latent TB: Treatment may still be recommended to prevent future disease. Many treatment plans are shorter — around three to four months. Your physician will weigh the benefits and risks based on your overall health and exposure risk.
Symptoms of active TB
Be alert for signs of active TB, including:
- Cough lasting three weeks or more, possibly with blood
- Night sweats, unexplained weight loss
- Chest pain, fatigue and fever
Where can I get a TB test?
You can get tested for TB at your local health department or at your primary care provider's office. Your provider will decide the best TB test for you. Public and private health care plans may cover TB testing costs.
At Scripps, TB testing is available at Scripps HealthExpress walk-in clinics located at Scripps Clinic and Scripps Coastal Medical Center throughout San Diego County, as well as at your Scripps primary care physician’s office.
When to seek help
If you are not sure about needing a test, or if you have a positive test, talk to your doctor. With quick testing and care, latent TB can be treated well before it becomes active.