Core Curriculum on Tuberculosis, 2000
Diagnosis of TB
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.
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.
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
- Determining how many people in a group are infected with M.
- 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.
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