There are two kinds of tests that can be used to help detect TB infection - the TB skin test (TST) and TB blood tests or Interferon-Gamma Release Assays (IGRAS) (i.e., QuantiFERON®-TB Gold test (QFT-G), QuantiFERON®-TB Gold In-Tube test (GFT-GIT) and T-SPOT®.TB test).
IGRAS and TSTs should be used as an aid in diagnosing infection with M. tuberculosis. A positive test result suggests that M. tuberculosis infection is likely; a negative result suggests that infection is unlikely. For IGRA test results either an indeterminate or borderline test result (T-SPOT® only) indicates an uncertain likelihood of M. tuberculosis infection.
A diagnosis of Latent Tuberculosis Infection (LTBI) requires that TB disease be excluded by medical evaluation. This should include checking for signs and symptoms suggestive of TB disease, a chest x-ray, and, when indicated, examination of sputum or other clinical samples for the presence of M. tuberculosis. Decisions about a diagnosis of M. tuberculosis infection should also include epidemiological and the patient’s medical history.
Tuberculin Skin Test
The TB skin test (Mantoux tuberculin skin test) is performed by injecting a small amount of fluid (called tuberculin) into the skin in the lower part of the arm. A person given the tuberculin skin test must return within 48 to 72 hours to have a trained health care worker look for a reaction on the arm.
Interferon-Gamma Release Assay (IGRA)
Interferon-gamma release assays (IGRAs) are blood tests that measure how the immune system reacts to the bacteria that cause TB. If your health care provider or local health department offers TB blood tests, only one visit is required to draw blood for the test. The QuantiFERON®-TB Gold test (QFT-G), QuantiFERON®-TB Gold In-Tube test (GFT-GIT) and T-SPOT®.TB test are approved TB blood tests by the Food and Drug Administration.
BCG, or Bacille Calmette-Guérin, is a vaccine for TB disease. Many persons born outside of the United States have been BCG-vaccinated. BCG is used in many countries with a high prevalence of TB to prevent childhood tuberculous meningitis and miliary disease.
Testing and Treatment for TB in BCG-Vaccinated Persons
The question of the effect of BCG vaccine on TST results often causes confusion. TST reactivity caused by BCG vaccine generally wanes with the passage of time, but periodic skin testing may prolong (boost) reactivity in vaccinated persons. A history of BCG vaccine is not a contraindication for tuberculin skin testing or treatment for LTBI in persons with positive TST results. TST reactions should be interpreted regardless of BCG vaccination history.
IGRAs use M. tuberculosis specific antigens and, unlike the TB skin tests, are not affected by prior BCG vaccination and are not expected to give a false-positive result in persons who have received prior BCG vaccination.
Class B Tuberculosis Follow-up
Information regarding Tuberculosis Class B Follow-up Worksheets can be found on the Iowa HHS Refugee Health web page.
TST and Vaccine Administration
From the CDC's 14th Edition of the "Pink Book" Epidemiology and Prevention of Vaccine-Preventable Diseases:
"Persons who need a tuberculin skin test (TST) can and should be vaccinated. All vaccines can be administered on the same day as a TST or at any time after a TST is administered. For most vaccines, there are no TST timing restrictions.
MMR-containing vaccine may decrease the response to a TST, potentially causing a false-negative response in someone who has a tuberculosis infection. MMR-II can be administered the same day as a TST, but if MMR-II has been administered and 1 or more days have elapsed, it is recommended in most situations to wait at least 4 weeks before administering a routine TST. There is no information available on the effect of varicella-containing vaccine or FluMist on a TST. Until such information is available, it is prudent to apply the same rules for spacing measles-containing vaccine and TST to varicella-containing vaccine and FluMist.
An interferon-gamma release assay (IGRA) tuberculosis test may be affected by live vaccines, so it is prudent to apply the same spacing rules as for TST and live vaccines."
Both clinically suspected and laboratory confirmed tuberculosis disease are to be reported.
- Cases of both pulmonary and extrapulmonary disease should be reported to Iowa HHS within one working day.
- Latent tuberculosis infection (LTBI) is not reportable in Iowa, however Iowa HHS does provide medication to treat LTBI to prevent progression to disease.
Iowa HHS provides medication free of charge to treat both LTBI and TB disease. Click here for information on prescription services.
How to Report
TB Control Program
Phone: (515) 281-8636 or (515) 281-7504
24/7 disease reporting telephone hotline: 800-362-2736
Clinical specimens should be submitted to State Hygienic Laboratory at the University of Iowa.
UI Research Park - Coralville
Iowa City, IA 52242-5002
Phone: 319-335-4500 or 1-800-421-IOWA (4692)