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U.S. Department of Health and Human Services

  

Core Curriculum on Tuberculosis, 2000

Chapter 5
Diagnosis of TB

Medical Evaluation

A complete medical evaluation for TB includes a medical history, a physical examination, a Mantoux tuberculin skin test, a chest radiograph, and any appropriate bacteriologic or histologic examinations.

Medical History
The symptoms of pulmonary TB may include a productive, prolonged cough (duration of ³3 weeks), chest pain, and hemoptysis. Systemic symptoms of TB include fever, chills, night sweats, appetite loss, weight loss, and easy fatigability. TB should be considered in persons who have these symptoms.

Approximately 19% of TB cases are exclusively extrapulmonary. 1 The symptoms of extrapulmonary TB depend on the site affected. TB of the spine may cause pain in the back; TB of the kidney may cause blood in the urine. Extrapulmonary TB should be considered in the differential diagnosis of ill persons who have systemic symptoms and who are at high risk for TB.

It is important to ask persons suspected of having TB about their history of TB exposure, infection, or disease. Clinicians may also contact the local health department for information about whether a patient has received TB treatment in the past. If the drug regimen was inadequate or if the patient did not adhere to therapy, TB may recur and may be drug resistant. It is also important to consider demographic factors (country of origin, age, ethnic or racial group, occupation) that may increase the patientís risk for exposure to TB or to drug-resistant TB disease.

In addition, clinicians should determine whether the patient has medical conditions, especially HIV infection, that increase the risk for TB disease (see Transmission and Pathogenesis). All patients who do not know their current HIV status should be referred for HIV counseling and testing.

Physical Examination
A physical examination is an essential part of the evaluation of any patient. It cannot be used to confirm or rule out TB, but it can provide valuable information about the patientís overall condition and other factors that may affect how TB is treated.

Tuberculin Skin Testing
The tuberculin skin test is useful for

  • Examining a person who is not ill but may be infected with M. tuberculosis, such as a person who has been exposed to someone who has TB. The tuberculin skin test is the only way to diagnose TB infection before the infection has progressed to TB disease;
  • Determining how many people in a group are infected with M. tuberculosis;
  • Examining a person who has symptoms of TB.

The preferred method of testing for TB infection in adults and children is the Mantoux tuberculin skin test. The administration of tuberculin using the Mantoux method and interpretation of its results are discussed in Testing for TB Disease and Infection.

As noted in Testing for TB Disease and Infection, a negative reaction to the tuberculin skin test does not exclude the diagnosis of TB, especially for patients with severe TB illness or infection with HIV. Also, some persons may not react to the tuberculin skin test if they are tested too soon after being exposed to TB. In general, it takes 2 to 10 weeks after infection for a person to develop an immune response to tuberculin. Persons who have recently been around someone with TB and who have a negative reaction to the tuberculin skin test should be retested 10 to 12 weeks after the last time they were exposed to infectious TB. Children younger than 6 months of age may not react to the tuberculin skin test because their immune systems are not yet fully developed.

Chest Radiograph
A posterior-anterior radiograph of the chest is the standard view used for the detection and description of chest abnormalities. In some instances, other views (e.g., lateral, lordotic) or additional studies (e.g., CT scans) may be necessary.

In pulmonary TB, radiographic abnormalities are often seen in the apical and posterior segments of the upper lobe or in the superior segments of the lower lobe. However, lesions may appear anywhere in the lungs and may differ in size, shape, density, and cavitation, especially in HIV-positive and other immunosuppressed persons.

In HIV-infected persons, pulmonary TB may present atypically on the chest radiograph. For example, TB may cause infiltrates without cavities in any lung zone, or it may cause mediastinal or hilar lymphadenopathy with or without accompanying infiltrates and/or cavities. In HIV-positive persons, almost any abnormality on a chest radiograph may indicate TB. In fact, the radiograph of an HIV-positive person with TB disease may even appear entirely normal.

Old healed tuberculosis usually presents a different radiographic appearance from active tuberculosis. Old healed tuberculosis can produce various radiographic findings. Dense pulmonary nodules, with or without visible calcification, may be seen in the hilar area or upper lobes. Smaller nodules, with or without fibrotic scars, are often seen in the upper lobes. Upper-lobe volume loss often accompanies these scars. Nodules and fibrotic lesions of old healed tuberculosis have well-demarcated, sharp margins and are often described as "hard." Bronchiectasis of the upper lobes is a nonspecific finding that sometimes occurs from previous pulmonary tuberculosis. Pleural scarring may be caused by old tuberculosis, but is more commonly caused by trauma or other infections.

Nodules and fibrotic scars may contain slowly multiplying tubercle bacilli with the potential for future progression to active tuberculosis. The risk of progression is significant, and persons who have nodular or fibrotic lesions consistent with findings of old tuberculosis on chest radiograph and have a positive tuberculin skin test reaction should be considered high-priority candidates for treatment of latent infection regardless of age. Conversely, calcified nodular lesions (calcified granuloma) pose a very low risk for future progression to active tuberculosis.

Abnormalities on chest radiographs may be suggestive of, but are never diagnostic of, TB. However, chest radiographs may be used to rule out the possibility of pulmonary TB in a person who has a positive reaction to the tuberculin skin test and no symptoms of disease.

 


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

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