Get Your Free TB Skin Test Information Guide

What TB Skin Tests Are and How They Work

A TB skin test, also called a tuberculin skin test (TST) or Mantoux test, is a simple medical procedure used to detect whether someone has been exposed to tuberculosis bacteria. The test involves injecting a small amount of fluid called tuberculin under the top layer of skin on the forearm. A nurse or medical professional performs this injection, which takes just a few seconds and causes minimal discomfort—most people describe it as a quick pinch.

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The test works by measuring how your body's immune system responds to tuberculin. After the injection, you must wait 48 to 72 hours and then return to have a healthcare provider examine the injection site. The provider measures any raised bump or hardening that appears on your skin. The size of this bump indicates whether you may have been infected with tuberculosis bacteria at some point. A larger bump generally suggests past or current TB infection, while no bump or a very small bump suggests you have not been infected.

It is important to understand that a positive TB skin test does not automatically mean you have active tuberculosis disease. Many people who test positive have latent TB infection, which means the bacteria are in their body but not causing illness. Active TB disease occurs when the bacteria multiply and damage the lungs or other organs, causing symptoms like cough, fever, and chest pain. Only a doctor can determine which situation applies to you through additional testing and evaluation.

The TB skin test has been used for over a century and remains one of the most common screening tools worldwide. According to the Centers for Disease Control and Prevention (CDC), TB skin tests are used to screen millions of people annually in healthcare settings, schools, workplaces, and community health clinics. The test is relatively inexpensive, requires no special equipment beyond the tuberculin and a measuring device, and provides results that help guide medical decisions.

Practical Takeaway: Understanding that a TB skin test is a screening tool—not a diagnosis—helps you approach the procedure with accurate expectations. The test shows whether your body has encountered TB bacteria, but further medical evaluation determines whether you have latent or active infection.

Who Should Consider Getting a TB Skin Test

Certain groups of people benefit from TB skin testing because they have higher risk of exposure to tuberculosis or higher risk of developing active TB disease if infected. Healthcare workers represent one significant group. Nurses, doctors, laboratory technicians, and other medical staff work with patients who may have TB, making regular screening an important part of occupational health. Many hospitals and clinics require their staff to receive TB skin tests as part of employment requirements.

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People who have had close contact with someone diagnosed with active tuberculosis should also be tested. Close contact typically means spending significant time in the same household or sharing air space with an infected person for an extended period. If someone you live with or spend considerable time around has been diagnosed with TB disease, your doctor may recommend testing to determine if you have been exposed. This is particularly important because TB spreads through airborne droplets when an infected person coughs, sneezes, or speaks.

Individuals with compromised immune systems face greater risk of developing active TB if they have been infected. This group includes people living with HIV/AIDS, those taking medications that suppress the immune system, and people with certain chronic illnesses. For these individuals, a positive TB skin test may prompt preventive treatment to reduce their risk of developing active disease. The CDC estimates that people living with HIV are 18 times more likely to develop active TB than those without HIV.

Other groups for whom TB testing may be recommended include people born in countries with high TB rates, those living in crowded conditions such as shelters or correctional facilities, people who inject drugs, healthcare facility residents, and those working in facilities that serve high-risk populations. Additionally, recent immigrants or refugees from countries where TB is common may be screened as part of medical evaluation. Some employers, schools, and childcare facilities require TB testing before starting work or enrollment.

The information guide describes these various risk categories in detail, helping individuals understand whether they fall into a group for which testing is typically recommended. However, only a healthcare provider can assess your individual circumstances and recommend whether testing is appropriate for you.

Practical Takeaway: Review the risk categories in the guide to understand whether your work environment, living situation, health status, or background suggests that TB skin testing would be worthwhile for you to discuss with a healthcare provider.

Where to Obtain a TB Skin Test

TB skin tests are available through many different healthcare settings, making them relatively accessible to most people. Your primary care physician's office is one common location where you can receive a TB skin test. If you have a regular doctor, calling their office to ask about TB testing is a straightforward first step. Many family medicine practices, internal medicine offices, and pediatric practices offer this service as part of their routine care.

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Public health departments maintain clinics that offer TB skin testing, often at no cost or low cost to residents. These departments serve as critical resources for TB screening and prevention in communities. You can locate your local health department through your state or county government website. Public health clinics may operate on a walk-in basis or by appointment, and they typically serve people regardless of insurance status or ability to pay.

Community health centers and Federally Qualified Health Centers (FQHCs) provide TB skin testing as part of their services. These centers serve uninsured and underinsured populations and adjust fees based on income. You can find community health centers through the National Association of Community Health Centers website or by searching for "community health center" in your area. Many of these facilities have evening or weekend hours to accommodate working individuals.

Urgent care clinics and walk-in medical centers frequently offer TB skin testing without requiring an appointment. These facilities can be helpful if you need testing quickly and cannot wait for an appointment with your regular doctor. However, keep in mind that you will need to return 48 to 72 hours later to have the test read, so you should choose a location convenient for both visits.

Workplace health clinics, school-based health centers, and occupational health services provide TB testing when required for employment or enrollment. Some employers cover the cost of testing as part of health benefits. Universities often test students and staff through their health services offices. Correctional facilities, homeless shelters, and residential treatment programs also offer TB testing to residents and staff.

Practical Takeaway: Create a list of TB testing locations in your area—including your doctor's office, the local health department, and nearby community health centers—so you know where you can go if testing is recommended to you.

What to Expect During and After TB Skin Testing

The actual TB skin test procedure takes only a few minutes from start to finish. When you arrive, a healthcare provider will clean a small area on your forearm with alcohol and allow it to dry. Using a small needle attached to a tuberculin syringe, the provider injects tuberculin just under the surface of your skin. You will feel a slight pinch or pressure, but the injection causes minimal pain. The provider will then apply a small bandage if desired, though this is not necessary.

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After the injection, you can immediately resume your normal activities. You can wash the area, exercise, work, and go about your day without restriction. The injection site may feel slightly irritated or itchy, but you should not scratch it, as this can interfere with test results. Some people experience a small red mark at the injection site within a few hours, which is normal.

The critical part of TB skin testing is the reading that occurs 48 to 72 hours after injection. You must return to the same clinic or facility where you received the injection during this window. A healthcare provider will examine your forearm and measure the size of any bump (called induration) that has appeared. The provider uses a ruler or measuring device and records the measurement in millimeters. This measurement determines whether your test result is considered positive, negative, or borderline.

The interpretation of test results depends on several factors, including your health status and risk factors. According to CDC guidelines, an induration of 5 millimeters or larger may be considered positive for people with HIV infection, those in close contact with TB patients, and those with abnormal chest X-rays suggesting TB. For healthcare workers and other groups with lower risk, 10 millimeters may be the threshold for a positive result. For people with no known risk factors, 15 millimeters may indicate a positive result. Your healthcare provider will explain what your specific measurement means.

After the test is read, you will receive written results. If your test is negative, you likely do not have TB