Tuberculosis (TB) testing determines if an individual has been infected with Mycobacterium tuberculosis, the bacteria that causes the disease. Although TB rates have declined, testing remains an important public health measure for certain populations and occupational groups. Understanding where to access reliable screening and what the results mean is the first step toward managing a potential infection.
The Two Main Types of TB Tests
TB screening primarily uses two methods to check for the body’s immune response to the bacteria. Both tests look for evidence of infection but cannot distinguish between latent TB infection (LTBI) or active TB disease; they only confirm exposure.
The Tuberculin Skin Test (TST), also known as the Mantoux test, involves injecting a small amount of purified protein derivative (PPD) into the inner forearm. A healthcare professional measures the reaction—the size of the raised, hard bump—between 48 and 72 hours later. The TST requires the patient to make two separate visits to the testing location.
The Interferon Gamma Release Assay (IGRA) is a blood test, such as QuantiFERON or T-SPOT. These tests measure how immune cells react to TB-specific antigens in a laboratory setting. The IGRA requires only a single blood draw visit and is not affected by prior Bacille Calmette-Guérin (BCG) vaccination, which can cause a false positive TST result. The choice between TST and IGRA depends on factors like age, medical history, and the likelihood of the person returning for a follow-up reading.
Where to Seek Testing Services
Testing for TB is widely available across different healthcare settings, making it accessible for those who need screening for work, school, or travel requirements. The most common location is a primary care provider’s office, where testing can be integrated into a routine physical exam. This option is often preferred for convenience and allows the patient to discuss their medical history and risk factors with a familiar doctor.
Many local public health departments and community health centers also offer TB testing services. These facilities frequently provide tests at a reduced cost or sometimes for free, especially for individuals who are uninsured or considered to be at higher risk for infection.
Retail clinics, often situated within pharmacies, provide another convenient option for TB screening. These locations typically offer flexible, walk-in hours, which is helpful for individuals who need rapid testing. However, they primarily offer the TST, meaning a return visit for the reading is necessary.
Specialized laboratory services and private diagnostic companies, such as Labcorp or Quest Diagnostics, offer IGRA blood tests. This can be a fast option for those requiring a blood test for pre-employment or enrollment screening. Testing may also be available through occupational health services or university health centers for screened populations, such as healthcare workers or students.
Interpreting Results and Follow-Up Care
A positive result from a TST or an IGRA test signifies that the individual has been infected with TB bacteria at some point. This initial positive screen does not automatically mean the person has active TB disease, which is the contagious and symptomatic form of the infection. Instead, it most often indicates a Latent TB Infection (LTBI), where the immune system has contained the bacteria, preventing it from multiplying and causing illness.
Individuals with LTBI are asymptomatic, are not contagious, and usually have a normal chest X-ray. Untreated LTBI carries a risk of progressing to active TB disease, especially if the immune system is weakened. If the screening test is positive, the next step involves a medical evaluation, typically including a chest X-ray and a review of symptoms, to exclude the possibility of active disease.
If the chest X-ray is abnormal or if the person reports symptoms like a persistent cough, fever, or unexplained weight loss, further testing is required to diagnose active TB. These advanced tests may include collecting sputum samples for microscopic examination and culture. Treatment for LTBI is preventative and usually involves a course of antibiotics for several months. Active TB disease requires a more intensive regimen involving a combination of multiple drugs for at least six months.