Getting tested for tuberculosis starts with a doctor visit or a public health clinic

You cannot diagnose tuberculosis on your own. A healthcare provider must order a test, interpret the results, and determine whether you have active TB disease or latent TB infection. The most common first step is a skin test (also called a Mantoux test or tuberculin skin test), which takes about 15 minutes and costs little or nothing at a public health department. A blood test called an interferon-gamma release assay (IGRA) is faster and more accurate but less widely available. If either test is positive, a chest X-ray and sometimes a sputum sample will follow to confirm whether you have active disease.

You do not need insurance or a regular doctor to get tested. Public health departments in every state offer free or low-cost TB testing. Call your local health department directly, or use the CDC's clinic finder at cdc.gov/tb to locate the nearest testing site. If you have symptoms—persistent cough, chest pain, fever, night sweats, or weight loss lasting more than three weeks—tell the clinic when you call, because they may fast-track you or ask you to come at a specific time to prevent spread.

Key Takeaways

  • A skin test or blood test ordered by a healthcare provider is the only way to learn about you have TB; home tests do not exist.
  • Public health departments offer free TB testing regardless of insurance status or immigration status.
  • A positive skin or blood test does not mean you have active TB disease; a chest X-ray is needed to confirm.
  • If you have a persistent cough, fever, or night sweats lasting more than three weeks, tell the clinic so they can prioritize your appointment.
  • Results from a skin test take 48 to 72 hours; blood test results usually come back within one to two weeks.

The skin test: how it works and what the result means

The skin test involves an injection of a small amount of purified protein derivative (PPD) into the inner forearm. You feel a slight pinch, and a small bump appears immediately. You then return 48 to 72 hours later so the nurse can measure the bump. A bump larger than a certain size means the test is positive—your immune system has reacted to TB bacteria. The size threshold that counts as positive depends on your risk factors: for someone with no known risk, a bump of 15 millimeters or larger is positive; for someone with HIV or recent close contact with active TB, 5 millimeters or larger is positive.

A positive skin test means you have been exposed to TB bacteria and your immune system has responded. It does not tell you whether the infection is latent (dormant, not contagious) or active (multiplying, contagious). That is why a positive skin test always leads to a chest X-ray. A negative skin test—a bump smaller than the threshold—usually means you do not have TB infection, though in rare cases (recent infection, severe immune suppression, or certain vaccines) a negative test can be misleading.

Blood tests: faster results and fewer false positives

An interferon-gamma release assay (IGRA) is a blood test that measures how your immune cells respond to TB antigens in a test tube. You give one blood sample, and results come back in one to two weeks. The test is more specific than the skin test—fewer false positives—and it is not affected by the BCG vaccine (a TB vaccine given in many countries outside the United States). IGRAs are increasingly the first choice at hospitals and large clinics, but many public health departments still use the skin test because it is cheaper and does not require a lab.

Like the skin test, a positive IGRA does not distinguish between latent and active TB. You will still need a chest X-ray to determine whether bacteria are actively multiplying in your lungs. Some clinics use both tests together if the first result is unclear or if the person has a very high risk of active disease.

Chest X-ray: confirming whether TB is active

If your skin test or blood test is positive, your doctor will order a chest X-ray to look for signs of active TB disease in the lungs. Active TB typically shows up as patches or cavities in the upper lobes of the lungs, though the appearance varies. The X-ray takes a few minutes and involves no injection or discomfort. Results are usually available within a day or two.

A normal chest X-ray in someone with a positive skin or blood test means you have latent TB infection—bacteria in your body that are not multiplying and cannot spread to others. An abnormal X-ray suggests active TB disease, and your doctor will order a sputum test (a sample of mucus you cough up) to confirm the diagnosis and check whether the bacteria are resistant to standard antibiotics. This step is critical because it determines your treatment plan.

Sputum tests and drug resistance screening

If your chest X-ray shows signs of active TB, you will be asked to provide a sputum sample—mucus you cough up into a cup—usually collected early in the morning when sputum is thickest. The sample is sent to a lab where technicians look for TB bacteria under a microscope and grow cultures to identify the exact strain. This process takes one to two weeks for initial results and up to six weeks for full drug resistance testing.

Drug resistance testing is essential because some TB strains do not respond to standard first-line antibiotics. Multidrug-resistant TB (MDR-TB) requires longer treatment with more medications and more side effects. Extensively drug-resistant TB (XDR-TB) is even harder to treat. Knowing the resistance pattern from the start allows your doctor to prescribe the right regimen and improves your chances of cure.

What happens after a positive test

If you have latent TB infection (positive test, normal X-ray), your doctor will discuss whether you should take preventive medication. People at high risk of developing active disease—those with HIV, recent contacts of active TB cases, or those with certain medical conditions—are usually offered treatment. Preventive treatment typically involves taking one or more antibiotics for three to nine months and prevents active disease from developing in about 90 percent of cases.

If you have active TB disease, your doctor will prescribe a combination of antibiotics, usually four drugs taken together for two months, followed by two drugs for four more months. You will need to take these medications exactly as prescribed, even though you will start feeling better after a few weeks. Incomplete treatment allows the bacteria to develop resistance and can lead to relapse. Your doctor or a nurse will monitor you throughout treatment with follow-up X-rays and sputum tests to confirm the infection is clearing.

Where to get tested if you have no doctor

Call your local or state health department and ask for TB testing. Every state health department has a TB control program and can direct you to a clinic. If you do not know the number, search online for "[your county] health department" or visit the CDC website at cdc.gov/tb/links/tboffices.htm, which lists health department contacts by state. Some community health centers and urgent care clinics also offer TB testing on a sliding fee scale based on income.

If you are homeless or have unstable housing, many cities have outreach programs that bring TB testing to shelters and encampments. If you are incarcerated, the facility is required to offer TB testing. If you work in healthcare, education, or childcare, your employer may offer free testing as part of occupational health screening. Do not delay testing because of cost or lack of insurance—TB is contagious, and early detection protects both you and people around you.

Frequently Asked Questions

How long does it take to learn about I have TB?

A skin test takes 48 to 72 hours for results. A blood test takes one to two weeks. If the first test is positive, a chest X-ray takes one to two days. If active TB is suspected, sputum testing takes one to two weeks for initial results and up to six weeks for drug resistance testing. Total time from first test to diagnosis can be two to eight weeks.

Can I have TB without symptoms?

Yes. Latent TB infection causes no symptoms and is not contagious. You can have latent TB for years or your whole life without ever developing active disease. Active TB disease usually causes a persistent cough, fever, night sweats, or weight loss, but some people have mild symptoms that develop slowly. Testing is the only way to know for sure.

What if my skin test is positive but my chest X-ray is normal?

This means you have latent TB infection—TB bacteria in your body that are not actively multiplying. You are not contagious and do not have active disease. Your doctor will discuss whether preventive medication is right for you based on your age, health conditions, and risk of developing active TB in the future.

Do I need to tell my employer or contacts if I test positive?

If you have latent TB, you do not need to tell anyone—it is not contagious. If you have active TB disease, your doctor or health department will contact people you spent time with while contagious and offer them testing. You are not required to disclose your status to your employer unless you work in healthcare or another setting where TB screening is part of the job.

Is the TB skin test accurate if I had the BCG vaccine?

The BCG vaccine can cause a positive skin test even if you do not have TB infection, making the result hard to interpret. If you received BCG (common outside the United States), ask your doctor about a blood test (IGRA) instead, which is not affected by the vaccine and gives a clearer answer.