A TB assessment is a systematic screening process used to determine whether you have been infected with tuberculosis and, if so, whether the infection is inactive (latent) or active disease. It typically combines a risk questionnaire, a blood or skin test, a symptom evaluation, and sometimes a chest X-ray. Most people encounter a TB assessment when starting a new healthcare job, enrolling in school, or entering certain institutional settings.
What a TB Assessment Includes
A full TB assessment can involve up to five components, though not everyone needs all of them. The CDC outlines these parts: a medical history review, a physical examination, a TB blood test or skin test, a chest X-ray, and lab work such as sputum cultures when active disease is suspected. For most people, the process starts with a risk questionnaire and a single test, then stops there if results are negative.
The risk questionnaire is the gateway step. It asks whether you were born in, traveled to, or lived for at least one month in a country with high TB rates. It asks about close contact with anyone who had infectious TB, any history of homelessness or incarceration, and whether you take medications that suppress your immune system. If none of those boxes apply, testing may not even be recommended. The CDC actively discourages testing people at low risk because positive results in that group are more likely to be false positives, leading to unnecessary follow-up and treatment.
The TB Skin Test
The tuberculin skin test (also called the Mantoux test or TST) involves a small injection just under the skin of your forearm. You return 48 to 72 hours later so a provider can measure any firm, raised bump that developed at the injection site. The size of that bump, measured in millimeters, determines whether your result counts as positive, and the threshold depends on your risk level.
For people with HIV, organ transplants, or significant immune suppression, a bump of 5 mm or larger is considered positive. For people born in countries where TB is common, those with diabetes or severe kidney disease, people who live or work in shelters or correctional facilities, and children under five, the threshold is 10 mm. For people with no known risk factors, only a bump of 15 mm or larger counts as positive.
One important limitation: the skin test can produce a false positive in people who received the BCG vaccine, which is routinely given in many countries outside the United States. If you were vaccinated as a child, a blood test is generally preferred.
The TB Blood Test
Two FDA-approved blood tests are available in the U.S.: QuantiFERON-TB Gold Plus and T-SPOT. Both measure how your immune cells respond to TB-specific proteins in a lab setting. They offer several practical advantages over the skin test. You only need one visit instead of two. Results are typically available within 24 hours. And critically, these tests are not affected by prior BCG vaccination, which eliminates a major source of false positives for people vaccinated overseas.
Blood tests also avoid the “booster phenomenon,” where repeated skin tests over time can artificially amplify results. For these reasons, many employers and clinics now default to blood testing.
What Happens if Your Test Is Positive
A positive blood or skin test means your body has encountered TB bacteria at some point. It does not mean you have active disease. The next step is distinguishing between inactive TB (latent infection) and active TB disease, and this is where the chest X-ray and symptom evaluation come in.
If you have a positive test result but no symptoms and a normal chest X-ray, you are typically diagnosed with inactive (latent) TB. You are not sick, you feel fine, and you cannot spread TB to others. Your provider will likely recommend a course of preventive treatment to keep the infection from becoming active in the future.
If you have symptoms along with a positive test and abnormal imaging, you may be evaluated for active disease. Symptoms of active pulmonary TB include a cough lasting three weeks or longer, chest pain, coughing up blood or phlegm, unexplained weight loss, fatigue, fever, chills, night sweats, and loss of appetite. TB can also affect other parts of the body: lymph node TB may cause firm, discolored swelling under the skin; TB in the kidneys can cause blood in the urine; TB in the spine can cause back pain; and TB meningitis can cause headache or confusion.
What the Chest X-Ray Shows
A chest X-ray is a standard part of TB evaluation when a test comes back positive or symptoms are present. Radiologists look for specific patterns that suggest active infection: areas of dense consolidation (white patches indicating inflamed lung tissue), usually concentrated in the upper portions of the lungs. Thick-walled cavities, which represent areas where the infection has destroyed lung tissue, are a hallmark of active TB. Small scattered nodules throughout both lungs can indicate the infection has spread through the bloodstream, a pattern called miliary TB. Fluid collection around one lung also suggests active disease.
Some findings point to old, healed TB rather than current infection. Calcified nodules and areas of scarring with no surrounding inflammation generally suggest a past infection that is no longer active. When X-ray findings are subtle or ambiguous, a CT scan may be needed for a clearer picture.
Lab Confirmation for Active Disease
When active TB is suspected, sputum samples are collected to look for TB bacteria directly. The standard approach calls for three early-morning deep-cough specimens collected on consecutive days, with each sample at least two milliliters in volume. These samples are examined under a microscope and sent for culture, which is the definitive test. Cultures take longer to produce results (sometimes weeks), but they confirm the presence of live TB bacteria and allow testing to determine which medications the bacteria will respond to.
TB Assessments for Healthcare Workers
If you work in healthcare, you will be screened for TB when you are hired. This baseline screening includes a risk assessment, a symptom check, and a TB blood or skin test. After that initial screening, routine repeat testing at set intervals (such as annually) is no longer recommended by the CDC unless there has been a known TB exposure at your facility or evidence of ongoing transmission. All healthcare workers should still receive annual TB education, and anyone exposed to a patient with active TB should be promptly re-evaluated with a symptom screen and testing.
Some facilities still choose annual screening for staff in higher-risk roles, such as pulmonologists, respiratory therapists, or emergency department workers. State regulations may also impose their own requirements that go beyond CDC recommendations, so workplace policies can vary.
Who Needs a TB Assessment
Beyond healthcare settings, TB assessments are commonly required for school enrollment, immigration medical exams, employment in congregate living facilities like nursing homes or shelters, and volunteer work in certain international settings. You may also be asked to complete one if you are starting a medication that suppresses your immune system, since latent TB can reactivate when immunity drops.
If you have no risk factors and are not in a situation that requires screening, a TB assessment is generally not necessary. Testing low-risk populations wastes resources and produces misleading results. The current guidance is clear: TB testing should follow a risk assessment, not replace one.