CDC Logo Tuberculosis Information CD-ROM   Image of people
jump over main navigation bar to content area
TB Guidelines
Surveillance Reports
Slide Sets
TB-Related MMWRs and Reports
Education/Training Materials
Ordering Information


U.S. Department of Health and Human Services


Education Materials > Publications > Self-Study Modules on TB > Module 3 > Background

Self-Study Modules on Tuberculosis

This is an archived document. The links are no longer being updated.

Module 3: Diagnosis of Tuberculosis Infection and Disease


In this module, you will learn about the diagnosis of TB infection and disease. TB infection is diagnosed with the tuberculin skin test. The purpose of diagnosing TB infection is to identify (1) people with TB infection who may be given treatment to prevent them from developing TB disease and (2) people who may have TB disease and who need treatment to be cured. In most cases, TB disease is diagnosed with certain laboratory tests (bacteriologic examination); for patients who may have pulmonary TB disease, a chest x-ray is also useful for diagnosis. It is important to evaluate people who have symptoms of TB disease; if they are found to have TB disease, they need treatment to be cured and to avoid spreading TB to others. For this reason, the diagnosis of TB disease is crucial to controlling the spread of TB in homes and communities.


After working through this module, you will be able to:
  1. Explain the purpose of the tuberculin skin test.
  2. Describe how the Mantoux tuberculin skin test is given.
  3. Explain when the patient's arm is examined and how the induration is measured.
  4. Explain why the Mantoux skin test is preferable to multiple-puncture tests.
  5. Explain how the reaction to the Mantoux skin test is classified.
  6. Describe the factors that can cause a false-positive reaction to the tuberculin skin test.
  7. Explain how reactions to the tuberculin skin test are interpreted for BCG-vaccinated persons.
  8. Describe the factors that can cause a false-negative reaction to the tuberculin skin test.
  9. Discuss why and for whom anergy testing should be considered.
  10. Describe the booster phenomenon.
  11. Discuss why and when two-step tuberculin testing should be done.
  12. List the four steps in diagnosing TB disease.
  13. List the parts of the medical history that should lead a clinician to suspect TB.
  14. Describe the symptoms of TB disease.
  15. Explain the purposes of the chest x-ray in diagnosing TB disease.
  16. List the four parts of a bacteriologic examination.
  17. Outline the procedures for collecting sputum specimens.
  18. Explain the purpose and significance of the acid-fast bacilli smear.
  19. Explain the purpose and significance of the culture.
  20. Explain the purpose and significance of drug susceptibility testing.

New Terms

Look for the following new terms in this module and in the glossary.

acid-fast bacilli (AFB) – mycobacteria that stay stained even after they have been washed in an acid solution; may be detected under a microscope in a stained smear

anergy – the inability to react to a skin test because of a weakened immune system, often caused by HIV infection or severe illness (see anergy testing)

anergy testing – giving skin tests using two substances other than tuberculin; done to determine whether a person is anergic. People who do not react to any of the substances, including tuberculin, after 48 to 72 hours (that is, people who have less than 3 millimeters of induration to all of the skin tests), are considered anergic.

bacteriologic examination – tests done in a mycobacteriology laboratory to diagnose TB disease; includes examining a specimen under a microscope, culturing the specimen, and doing drug susceptibility testing

baseline skin test – the tuberculin skin test given to employees or residents in certain facilities when they start their job or enter the facility (see TB screening program and two-step testing)

BCG – bacille Calmette-Guιrin (BCG), a vaccine for TB disease that is used in many countries but rarely used in the United States; may cause a false-positive reaction to the tuberculin skin test

boosted reaction – a positive reaction to a tuberculin skin test, due to a boosted immune response from a skin test given up to a year earlier; occurs in people who were infected a long time ago and whose ability to react to tuberculin had lessened. Two-step testing is used in TB screening programs to tell the difference between boosted reactions and reactions caused by recent infection (see booster phenomenon and two-step testing)

booster phenomenon – a phenomenon in which people (especially older adults) who are skin tested many years after becoming infected with M. tuberculosis may have a negative reaction to an initial skin test, followed by a positive reaction to a skin test given up to a year later; this happens because the first skin test boosts the immune response. Two-step testing is used in TB screening programs to tell the difference between boosted reactions and reactions caused by recent infection (see two-step testing)

bronchoscopy – a procedure used to obtain pulmonary secretions or lung tissue with an instrument called a bronchoscope; used only when patients cannot cough up sputum on their own and an induced specimen cannot be obtained

cavity – a hollow space within the lung, visible on a chest x-ray, that may contain many tubercle bacilli; often occurs in people with severe pulmonary TB disease

clinician – a physician, physician assistant, or nurse

colonies – groups of mycobacteria that have grown in a culture

culture – organisms grown on media (substances containing nutrients) so that they can be identified; a positive culture for M. tuberculosis contains tubercle bacilli, whereas a negative culture contains no detectable tubercle bacilli

drug susceptibility pattern – the list of drugs to which the strain of tubercle bacilli is susceptible and to which it is resistant

erythema – redness around the site of the injection when a Mantoux skin test is done; erythema is not considered when the reaction size is measured, because redness does not indicate that a person has TB infection

exposure to TB – time spent with someone who has infectious TB disease

false-negative reaction – a negative reaction to the tuberculin skin test in a person who has TB infection; may be caused by anergy, recent infection (within the past 10 weeks), or very young age (younger than 6 months old)

false-positive reaction – a positive reaction to the tuberculin skin test in a person who does not have TB infection; may be caused by infection with nontuberculous mycobacteria or by vaccination with BCG

gastric washing – a procedure done by inserting a tube through the patient's nose and passing it into the stomach; may be useful for obtaining sputum from children, who produce little or no sputum when they cough

induced sputum – sputum that is obtained by having the patient inhale a saline (salt water) mist, causing the patient to cough deeply; this procedure is used to help patients cough up sputum if they cannot do so on their own

induration – swelling that can be felt around the site of injection after a Mantoux skin test is done; the reaction size is the diameter of the swollen area (excluding any redness), measured across the forearm

infiltrate – a collection of fluid and cells in the tissues of the lung; visible on a chest x-ray in people with pulmonary TB disease

isolate – a group of organisms isolated, or separated, from a specimen; in an M. tuberculosis isolate, the organisms have been identified as M. tuberculosis (a positive culture for M. tuberculosis)

malaise – a feeling of general discomfort or illness

Mantoux tuberculin skin test – the preferred method of testing for TB infection; done by using a needle and syringe to inject 0.1 ml of 5 tuberculin units of liquid tuberculin between the layers of the skin (intradermally), usually on the forearm; the reaction to this test, usually a small swollen area (induration), is measured 48 to 72 hours after the injection and is classified as positive or negative depending on the size of the reaction and the patient's risk factors for TB

media – substances containing special nutrients for growing cultures of bacteria found in specimens

medical history – the part of a patient's life history that is important for diagnosing and treating TB infection or disease, including history of exposure, symptoms, diagnosis of TB infection or disease, and risk factors for TB disease

multiple-puncture test – tuberculin skin test done by puncturing the skin of the forearm with a set of short prongs or tines to inject tuberculin (for example, Tine test); although easy to give and convenient, these tests are not accurate and should not be used to determine whether a person has TB infection

mycobacteriology laboratory – a laboratory that deals specifically with M. tuberculosis and other mycobacteria

PPD skin test – a tuberculin skin test

purified protein derivative (PPD) – the type of tuberculin used in the Mantoux skin test

resistant – able to grow in the presence of a particular drug

skin test conversion – a change in a skin test reaction from negative to positive between screening intervals

smear – a specimen that has been smeared onto a glass slide, stained, washed in an acid solution, and then placed under the microscope for examination; used to detect acid-fast bacilli in a specimen

sputum – phlegm from deep in the lungs, collected in a sterile container for processing and examination

susceptible – able to be killed by a particular drug

symptoms of TB disease – conditions caused by TB disease. The symptoms of pulmonary TB disease include coughing, pain in the chest when breathing or coughing, and coughing up sputum or blood. The general symptoms of TB disease (pulmonary or extrapulmonary) include weight loss, fatigue, malaise, fever, and night sweats. The symptoms of extrapulmonary TB disease depend on the part of the body that is affected by the disease

TB screening program – a program in which employees and residents of a facility are periodically given tuberculin skin tests; done to identify people who have TB infection and possibly TB disease and to determine whether TB is being transmitted in the facility

tuberculin – protein from tubercle bacilli that have been killed by heating; used to determine whether a person has TB infection. Tuberculin is not a vaccine.

tuberculin unit – a standard strength of tuberculin used in the United States and Canada; a strength of 5 tuberculin units is used for the Mantoux tuberculin skin test

two-step testing – a strategy used in TB screening programs to distinguish a boosted reaction (caused by TB infection that occurred many years before the skin test) from a reaction caused by recent infection. If a person has a negative reaction to an initial skin test, a second test is given 1 to 3 weeks later; a positive reaction to the second test probably represents a boosted reaction, not recent infection. Two-step testing is used in many TB screening programs for skin testing employees when they start their job.


Released October 2008
Centers for Disease Control and Prevention
National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention
Division of Tuberculosis Elimination -

Please send comments/suggestions/requests to:, or to
CDC/Division of Tuberculosis Elimination
Communications, Education, and Behavioral Studies Branch
1600 Clifton Rd., NE - Mailstop E-10, Atlanta, GA 30333