Tuberculosis diagnosis

Main article: Tuberculosis

A complete medical evaluation for tuberculosis (TB) includes a medical history, a physical examination, a tuberculin skin test, a chest X-ray, and microbiologic smears and cultures.

Contents
1 Medical history
2 Physical examination
3 Chest X-ray
4 Laboratory
5 Microbiological studies
6 Tuberculin skin test

6.1 Mantoux skin test
6.2 Heaf test

7 Classification of tuberculin reaction
8 Contact screening
9 Tuberculosis classification system
10 References

Medical history

The medical history includes obtaining the symptoms of pulmonary TB: productive, prolonged cough of three or more weeks, chest pain, and hemoptysis. Systemic symptoms include fever, chills, night sweats, appetite loss, weight loss, and easy fatigability. Other parts of the medical history include prior TB exposure, infection or disease; past TB treatment; demographic risk factors for TB; and medical conditions that increase risk for TB disease such as HIV infection.

Tuberculosis should be suspected when a persistent respiratory illness in an otherwise healthy individual does not respond to regular antibiotics.

Physical examination

A physical examination is done to assess the patient's general health and find other factors which may affect the TB treatment plan. It cannot be used to confirm or rule out TB.

Chest X-ray

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Tuberculosis creates cavities visible in x-rays like this one in the patient's right upper lobe.

In active pulmonary TB, infiltrates or consolidations and/or cavities are often seen in the upper lungs with or without mediastinal or hilar lymphadenopathy or pleural effusions ( tuberculous pleurisy). However, lesions may appear anywhere in the lungs. In disseminated TB a pattern of many tiny nodules throughout the lung fields is common - the so called milliary TB. In HIV and other immunosuppressed persons, any abnormality may indicate TB or the chest X-ray may even appear entirely normal.

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.

See Tuberculosis radiology for more information.

Laboratory

QuantiFERON-Gold is a blood test that measures the patient’s immune reactivity to the TB bacteria and is useful for initial and serial testing of persons with a risk of latent tuberculosis infection (LTBI). QuantiFERON-Gold utilizes the TB specific antigens CFP10 and ESAT6 and therefore does not present fasle positive to the BCG vccination. A fact sheet from CDC is available.

The enzyme linked immunospot (ELISPOT) blood test is another blood test that may replace the skin test for diagnosis. PMID 14586040

Microbiological studies

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Distinctive clusters of colorless Mycobacterium tuberculosis form in this culture.

Sputum smears and cultures should be done for acid-fast bacilli if the patient is producing sputum. If no sputum is being produced,examination of gastric juice, a laryngeal swab, bronchoscopy or fine needle aspiration should be considered. Other mycobacteria are also AFB. Even if sputum smear is negative, tuberculosis must be considered and is only excluded after negative cultures. Further PCR or gene probe tests can distinguish M. tuberculosis from other mycobacteria. If this is not available, a culture of the AFB can distinguish the various forms of mycobacteria, although results from this may take four to eight weeks for a conclusive answer.

Tuberculin skin test

Two tests are available: the Mantoux and Heaf tests.

Mantoux skin test

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The Mantoux test for TB involves intradermally injecting PPD tuberculin and measuring the size of induration 48-72 hours later.

The Mantoux skin test is used in the United States and is endorsed by the American Thoracic Society and Centers for Disease Control and Prevention (CDC). Multiple puncture tests such as the Tine test are not recommended.

See: Mantoux test for further information
If a person has had a history of a positive tuberculin skin test, another skin test is not needed.

Heaf test

The Heaf test is used in the United Kingdom and is endorsed by the British Thoracic Society.

The equivalent Mantoux test positive levels done with 10 TU (0.1 ml 100 TU/ml, 1:1000) are

Classification of tuberculin reaction

An induration (palpable raised hardened area of skin) of more than 5-15 mm (depending upon the person's risk factors) to 10 Mantoux units is considered a positive result, indicating TB infection.

A tuberculin test conversion is defined as an increase of 10 or more mm within a 2-year period regardless of age.

Contact screening

When someone is diagnosed with tuberculosis, all their close contacts should be screened for TB with a tuberculin skin test or a chest x-ray or both.

Tuberculosis classification system

The current clinical classification system for TB (Class 0 to 5) is based on the pathogenesis of the disease.

The U.S. Citizenship and Immigration Services has an additional TB classification (Class A, B1, or B2) for immigrants and refugees developed by the Centers for Disease Control and Prevention (CDC). The (Class) B notification program is an important screening strategy to identify new arrivals who have a high risk for TB.

See Tuberculosis classification for more details.

References

See also: Tuberculosis diagnosis, Bronchoscopy, CDC, Centers for Disease Control and Prevention, Corticosteroid, Diabetes, Heaf test, Hemoptysis, Human lung, Immigrant