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Education Materials > Publications > Self-Study Modules on TB > Module 3 > Diagnosis of TB Disease

Self-Study Modules on Tuberculosis

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Module 3: Diagnosis of Tuberculosis Infection and Disease

Diagnosis of TB Disease

Before clinicians can diagnose TB disease in a patient, they must think of the possibility of TB when they see a patient with symptoms of TB or abnormal chest x-ray findings. Because TB is not as common as it was many years ago, many clinicians do not consider the possibility of TB when making diagnoses for patients who have symptoms of TB. When this happens, the diagnosis of TB may be delayed or even overlooked, and the patient will remain ill and possibly infectious.

Anyone with symptoms of TB should be evaluated for TB disease. In addition, anyone found to have a positive tuberculin skin test reaction should be evaluated for TB disease.


There are four steps in diagnosing TB disease.

  1. The medical history. A medical history is the part of a patient's life history that is important for diagnosing and treating the patient's medical condition. It includes social, family, medical, and occupational information about the patient. To obtain a medical history, the clinician should ask whether the patient has:
    1. Been exposed to a person who has infectious TB
    2. Symptoms of TB disease
    3. Had TB infection or TB disease before
    4. Risk factors for developing TB disease

    Clinicians should suspect TB disease in patients with any of these factors.

  2. The tuberculin skin test. Patients with symptoms of TB disease are often given a tuberculin skin test. However, they should always be evaluated for TB disease, regardless of their skin test results. Furthermore, clinicians should not wait for tuberculin skin test results when evaluating patients who have symptoms of TB disease. Instead, they should give the patient a tuberculin skin test at the same time as they start the other steps in the diagnosis of TB disease.

  3. The chest x-ray. If the patient has TB disease in the lungs, the chest x-ray usually shows signs of TB disease.

  4. The bacteriologic examination. This is the examination and the culture (growth) of clinical specimens (for example, sputum or urine) in the laboratory. The bacteriologic examination has four parts:
    1. Obtaining a specimen
    2. Examining the specimen under a microscope
    3. Culturing the specimen
    4. Doing drug susceptibility testing on positive cultures


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

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