A TB test screens for infection with Mycobacterium tuberculosis, the bacteria responsible for tuberculosis. People often seek testing for requirements related to employment, international travel, or academic programs. Testing is also recommended following known exposure to an individual with active tuberculosis disease. These tests identify the presence of the bacteria but cannot immediately distinguish between a latent (dormant) infection and an active, contagious disease.
Choosing the Right TB Test
Two primary methods are available: the Tuberculin Skin Test (TST), also known as the purified protein derivative (PPD) test, and the Interferon-Gamma Release Assay (IGRA), a blood test. The TST involves injecting a small amount of tuberculin under the skin, typically on the forearm. It requires a follow-up visit between 48 and 72 hours later to check for a reaction. A positive result is indicated by induration, a raised, firm area of swelling measured by the healthcare provider.
The IGRA is a single-visit procedure requiring a blood draw, which is sent to a laboratory for analysis. This test measures the immune system’s reaction to TB proteins in the sample. The IGRA is often preferred for individuals who have received the Bacille Calmette-Guérin (BCG) vaccine. The BCG vaccine, given in some countries, can cause a false-positive result on the TST but does not affect the IGRA’s accuracy.
Where to Access TB Testing Services
The most common starting point for obtaining a TB test is your established Primary Care Provider (PCP). Your PCP’s office is equipped to administer either the TST or the IGRA and is familiar with your medical history, which aids in interpreting results. Testing at a PCP’s office is suitable for routine screening and may be covered under standard health insurance plans.
Urgent Care centers or retail health clinics offer convenient access, often with extended hours and no appointment required. However, if you opt for the TST at one of these sites, you must ensure you can return to the same facility within the required 48- to 72-hour window for the reading.
Public Health departments and specialized TB clinics are reliable options, particularly for those who are uninsured or require lower-cost testing. These clinics focus on infectious disease screening and may offer the IGRA blood test, eliminating the need for a second visit. They are also suitable if you are seeking consultation due to a known exposure or high-risk setting.
For students and employees, testing is frequently offered through institutional services. University Health Services provides testing to enrolled students, and Occupational Health departments manage screening for employees, particularly those in healthcare settings. These sites specialize in meeting compliance requirements and may offer streamlined testing processes.
Preparation and Understanding Your Results
Before your appointment, contact the facility to confirm which type of TB test they offer and verify the cost, especially if paying out-of-pocket. If using insurance, check in advance if the procedure is covered and if a referral is needed, as IGRA costs can be higher than the TST. If you receive the TST, carefully schedule the follow-up visit for the reading, as missing the 72-hour window requires the test to be restarted.
A positive result from either the TST or IGRA indicates infection with TB bacteria. This result does not automatically mean you have active, contagious tuberculosis disease; it only confirms the presence of the infection. Most people with a positive screen have latent TB infection, where the bacteria are present but inactive, causing no symptoms and preventing spread to others.
If your initial test is positive, your healthcare provider will order additional tests to determine if the infection is latent or active. Follow-up steps typically include a chest X-ray and, in some cases, a sputum test, which analyzes mucus from the lungs. Following this evaluation, a treatment plan, often involving medication for several months, will be recommended to prevent a latent infection from progressing into active TB disease.