Self-Study Modules on Tuberculosis
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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
There are four steps in diagnosing TB disease.
- 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:
- Been exposed to a person who has infectious TB
- Symptoms of TB disease
- Had TB infection or TB disease before
- Risk factors for developing TB disease
Clinicians should suspect TB disease in patients with any of
- 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.
- The chest x-ray.
If the patient has TB disease in the lungs, the chest x-ray usually
shows signs of TB disease.
- 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:
- Obtaining a specimen
- Examining the specimen
under a microscope
- Culturing the specimen
- 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 - http://www.cdc.gov/tb
Please send comments/suggestions/requests
CDC/Division of Tuberculosis Elimination
Communications, Education, and Behavioral Studies Branch
1600 Clifton Rd., NE - Mailstop E-10, Atlanta, GA 30333