Latent tuberculosis screening

People at increased risk, and not people at low risk. The two bodies draw the risk group differently.

USPSTF (2023) grades screening B for asymptomatic adults 18 or older at increased risk, and names two groups: "persons who were born in, or are former residents of, countries with high tuberculosis prevalence and persons who live in, or have lived in, high-risk congregate settings (eg, homeless shelters or correctional facilities)". It reports that in 2020, 71.5% of all active TB cases in the US occurred among persons born outside the US, and, citing CDC, that TB disease is common in most countries in Latin America, the Caribbean, Africa, Asia, Eastern Europe and Russia. The recommendation "does not apply to adults with symptoms of TB or to children and adolescents"; CDC (2025) says people with symptoms "should be evaluated for TB disease." USPSTF also names groups it did not review. People with immunosuppression (HIV, immunosuppressive medications, an organ transplant) and people with silicosis were left out because screening there may be considered standard care; contacts of people with active TB, health care workers and congregate-setting workers because their screening is part of public health or employee health surveillance. For diabetes, USPSTF found the evidence insufficient for a separate recommendation.

CDC (page updated April 2025) recommends testing people at increased risk, at any age, in two categories. Higher risk of exposure: contacts of people with infectious TB; people born in or who frequently travel to countries where TB disease is common; current or former residents of shelters, correctional facilities or nursing homes; employees of high-risk congregate settings; health care workers who serve patients with TB disease; locally defined higher-incidence populations; and infants, children and adolescents exposed to adults at increased risk. Higher risk of TB disease once infected: people with HIV; children younger than 5; anyone infected within the last 2 years; people with untreated or inadequately treated past TB disease; people on immunosuppressive therapy, including TNF-alpha antagonists, systemic corticosteroids equivalent to 15 mg or more of prednisone a day, or transplant drugs; people with silicosis, chronic renal failure, leukemia, or cancer of the head, neck or lung; people with diabetes mellitus; people who have had a gastrectomy or jejunoileal bypass; people under 90% of ideal body weight; and people who use substances such as injection drugs.

Low risk: CDC (2025) is explicit: "People who are at low risk generally should not be tested because the predictive value of a positive result is lower." Testing them raises the number of false positives, which send people through unnecessary evaluation and treatment, and CDC "discourages a testing approach that is independent of a risk assessment." The exception it names is testing required for employment or school attendance. USPSTF makes no statement about adults who are not at increased risk.

The blood test (IGRA) takes one visit. CDC: "Only one visit is required to draw blood for the test." CDC's IGRA page (2024) lists the blood test as "Unaffected by the bacille Calmette-Guérin (BCG) TB vaccine and most nontuberculosis mycobacteria".

The skin test (TST) takes two visits. CDC: "The TB skin test is performed by injecting 0.1 ml of tuberculin purified protein derivative (PPD) into the inner surface of the forearm." It is read "between 48 and 72 hours after administration by a health care worker trained to read TB skin results", and "A patient who does not return within 72 hours will need to be rescheduled for another skin test." The reader measures the firm swelling (induration) in millimeters, not the redness, against a cutoff set by your risk: CDC counts 5 mm or more as positive in groups such as people with HIV and recent contacts, 10 mm or more in groups such as people born in countries where TB disease is common, and 15 mm or more in "People with no known risk factors for TB".

Timing can change a result. CDC says it takes 2 to 8 weeks after infection for the immune system to produce a response either test can detect, so a negative blood test in a contact of someone with infectious TB is confirmed with a repeat test 8 to 10 weeks after the last exposure. Live-virus vaccines such as measles, mumps and rubella may interfere with test reactions, so CDC advises testing on the same day as the vaccine or at least one month after it. People with written documentation of a previous positive TB test, or of treatment for TB disease, are not tested again. CDC: "Most people who have a positive TB test result will continue to have a positive test result."

A positive test is not yet a diagnosis. Active TB has to be ruled out first. CDC: "A positive result from a TB blood test or TB skin test usually means TB infection. More tests, such as a chest radiograph, are needed to rule out TB disease." CDC's evaluation covers medical history, physical examination, the test for TB infection, a chest radiograph, and bacteriologic testing. USPSTF (2023) agrees that these additional examinations "are essential to completing a diagnosis of LTBI." Latent infection is diagnosed when the test is positive and the evaluation does not indicate TB disease.

For someone with no symptoms, CDC treats a normal chest X-ray as generally enough: "Normal findings on chest radiography generally can be used to rule out pulmonary TB in a person who has had a positive reaction to a TB blood test or TB skin test and no symptoms of disease." CDC notes rare exceptions in people with HIV whose immune status has not been restored by antiviral treatment. CDC: "TB disease must be excluded before initiating treatment for latent TB infection. Failure to do so may result in treatment failure and development of drug resistance."

Once active TB is excluded, CDC (2025): "People with latent TB infection should be treated to prevent the development of TB disease." CDC and the National Tuberculosis Coalition of America "preferentially recommend short-course, rifamycin-based, 3- or 4-month latent TB infection treatment regimens over 6- or 9-month isoniazid monotherapy", because short courses are effective and safe and more people finish them. The short regimens CDC names are three months of once-weekly isoniazid plus rifapentine (3HP), four months of daily rifampin (4R) and three months of daily isoniazid and rifampin (3HR), with longer isoniazid courses as alternatives. CDC states that treatment for latent TB infection is 90% effective for preventing the development of TB disease.

Limits a reader should know, from CDC's treatment page: 3HP is not recommended for pregnant women or women expecting to become pregnant during the three-month regimen, or for children younger than two. Rifamycins change the metabolism of many other medications, and "People who use hormonal birth control should be advised to add or switch to a barrier method." The 2020 guideline from CDC and the National Tuberculosis Controllers Association warns that rifampin and rifapentine are not interchangeable. CDC asks for a check at least monthly, on treatment, for adherence, symptoms of TB disease and side effects.