Seeking a tuberculosis (TB) test screens for the presence of the Mycobacterium tuberculosis bacteria. This screening helps identify infected individuals, even those without symptoms of active disease. Understanding where to get tested is the first step, which can lead to treatment for latent infection and prevent the bacteria from developing into a contagious illness. The test indicates whether your body has mounted an immune response to the bacteria, but it is not a diagnosis of active TB. Accessing this screening is straightforward, with options ranging from routine healthcare providers to specialized public health services.
Types of Tuberculosis Tests
Two primary methods screen for TB infection, both detecting the body’s immune reaction. The first is the Tuberculin Skin Test (TST), also called the Mantoux or PPD test, which involves injecting a small amount of purified protein derivative (PPD) beneath the skin of the forearm. If infected, immune memory cells react, requiring a return visit 48 to 72 hours later to measure the resulting induration, or firm swelling.
The second method is the Interferon-Gamma Release Assay (IGRA), a blood test requiring a single visit for sample collection. Commercial IGRAs, such as QuantiFERON-TB Gold Plus or T-SPOT.TB, measure interferon-gamma released by white blood cells when exposed to TB-related antigens in a laboratory setting. This blood test is preferred for individuals who have received the Bacille Calmette-Guérin (BCG) vaccine, as the TST can produce a false-positive result due to the vaccine’s components. The choice between tests often depends on medical history, age, and availability at the chosen location.
Primary Testing Locations
The most common route for obtaining a TB screening is through your Primary Care Physician’s office. These clinical settings routinely offer both the TST and IGRA tests for screening purposes. Scheduling a test here allows for continuity of care, integrating results directly into your medical record.
Urgent Care Centers and retail clinics, such as those inside pharmacies, offer TB testing services if you need a test quickly or without an appointment. These locations accommodate walk-in patients for the initial TST injection or a blood draw for the IGRA. It is advisable to confirm whether the center offers the TST, which requires a follow-up visit, or the IGRA, which is a one-time blood draw.
Local Public Health Departments are an excellent resource, particularly for low-cost or free testing options, especially in areas with a higher incidence of TB. Many public health clinics specialize in communicable disease screening and may offer walk-in testing. While some facilities have transitioned entirely to the IGRA blood test, others may still provide the TST and offer guidance on follow-up care if results are positive.
Specialized and Contextual Screening
In certain situations, TB screening is a mandated requirement tied to specific life events or professional roles. Many employers, especially those in healthcare, education, or correctional facilities, require a negative TB test as a condition of employment. Occupational health clinics or designated employee health services typically manage this process and specify which test, TST or IGRA, is required.
Students entering academic programs, particularly those in clinical fields, may also need to provide proof of a recent negative TB test for school entry. For individuals seeking immigrant or refugee status, the US Centers for Disease Control and Prevention (CDC) requires a medical examination performed by a designated civil surgeon. For immigration purposes, the IGRA blood test is frequently required instead of the TST, especially for applicants aged two years and older from high-TB burden countries.
Understanding the Testing Process and Results
The next step after initial screening depends on the type of test received. If you opt for the TST, you must return to the clinic for a reading between 48 and 72 hours after the injection. Missing this narrow window invalidates the test, requiring you to start the two-visit process over. The healthcare worker measures the induration—the hard, raised area, not just the redness—to interpret the result.
For the IGRA blood test, no return visit is necessary, but you must wait for the laboratory to process the sample. Results are typically available within three to five business days, though this timeframe varies by clinic and laboratory. Both TST and IGRA results are reported as either positive or negative, with a positive result meaning you have been infected with the TB bacteria.
A positive screening result most often indicates a latent TB infection (LTBI), not necessarily active, contagious tuberculosis disease. If your screening is positive, your provider will consult on the next steps, which includes a clinical evaluation and usually a chest X-ray to rule out active disease. If active disease is ruled out, your healthcare provider will discuss treatment options for LTBI to prevent the infection from progressing into a full-blown illness.