Tuberculosis Testing: How TB Tests Work

What a Tuberculosis Test Checks

Tuberculosis, often called TB, is caused by a bacterium that most often affects the lungs. Testing looks for the body's immune response to that bacterium. A positive result can mean one of two things. It may indicate latent TB, where the bacteria are inactive and you are not sick or contagious. It may also indicate active TB disease, where the bacteria are multiplying and you can pass the infection to others.

Finding latent TB matters because it can become active later. Testing helps identify people who would benefit from preventive treatment before they become ill.

Who Should Get Tested

Screening is recommended for people with a higher chance of exposure. This includes close contacts of someone with active TB, health care workers, people who live or work in crowded settings such as shelters or correctional facilities, and people who have lived in regions where TB is common. People with weakened immune systems, including those with HIV or on certain medicines, are also candidates.

Anyone with symptoms such as a persistent cough lasting more than three weeks, coughing up blood, night sweats, fever, or unexplained weight loss should be evaluated promptly. Symptoms of active TB need medical attention without delay.

Types of Tuberculosis Tests

Two main tests are used. The tuberculin skin test places a small amount of testing fluid under the skin of the forearm and is read 48 to 72 hours later. A raised, hardened area indicates a likely infection. The interferon gamma release assay is a blood test that measures the immune response to TB proteins. It requires only one visit and gives a result within one to two days.

The blood test is often preferred because it needs only a single visit and is not affected by prior BCG vaccination, which can cause a false positive on the skin test. A chest X ray and sputum tests are used when active TB is suspected.

How to Order and Where to Get Tested

You can ask your doctor for TB testing, visit a community clinics, or in most states order a TB blood test yourself through a direct access service. With self ordering you choose the test online, pay the listed price, and visit a CLIA certified lab for the blood draw. A licensed physician reviews the order, and results are shared with you.

Use a ZIP code search to find a nearby draw site, then check the hours and whether it takes walk ins. Bring a photo ID and your order confirmation. If you need a skin test instead, confirm that the location offers it, since not every site provides that service.

How Much Does Tuberculosis Testing Cost

Paying directly, a TB blood test commonly costs between $60 and $150. A skin test is often less expensive, but it requires a second visit for the reading. Prices vary by lab and region, so compare the listed price and check whether the draw fee is included.

Insurance often covers TB testing when it is ordered for a medical or occupational reason. If you have a high deductible, the direct cash price may be lower and is known up front. Community clinics often provide testing at low or no cost for people at higher risk.

Understanding Your Results

A negative result means the test did not find an immune response to TB. A positive result means you have been infected at some point, but it does not by itself show whether the infection is active. Further tests, such as a chest X ray and sputum samples, help tell the difference.

Do not start or stop any medicine based on a test result alone. Bring your report to a clinician who can interpret it and, if needed, arrange preventive or active treatment. Latent TB is usually treated to prevent it from becoming active later.

Treating Latent and Active TB

Treatment depends on whether the infection is latent or active. Latent TB is usually treated with a preventive course of medicine, which lowers the chance that the bacteria become active later. Active TB is treated with a combination of antibiotics taken for several months, and completing the full course is essential to avoid relapse and resistance.

During treatment for active TB, a clinician monitors your response and checks that the infection is no longer contagious. People with latent TB do not need to isolate, because they cannot spread the bacteria. Community clinics often provide testing and treatment at low or no cost, and they can help with contact tracing. If you are unsure which type of TB you have, a clinician can explain the results and the treatment options that fit your situation.