Tuberculosis diagnosis

Main article: Tuberculosis

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

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 examinationis 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

Image:TB CXR.jpg

In active pulmonary TB, infiltrates or consolidations and/or cavities are often seen in the upper lungswith 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 immunosuppressedpersons, 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 radiologyfor more information.

Laboratory

QuantiFERON-TB 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) or active tuberculosis disease. QuantiFERON-TB Gold utilizes the TB specific antigens CFP10 and ESAT6 and therefore does not present false positive to the BCG vaccination. Guidelinesfor the use of the FDA approved QuantiFERON-TB Gold were released by the CDC in December 2005.

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

Microbiological studies

Image:TB Culture.JPG Sputum smears and culturesshould 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, bronchoscopyor 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 PCRor 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.

Full blood count

Although a full blood countis never diagnostic, normocytic anemiaand lymphopeniaare common. Neutrophiliais rarely found.

Ureaand electrolytesare usually normal, although hypocalcemiaand hyponatremiaare possible in tuberculous meningoencephalitis due to SIADHS. In advanced disease, hypoalbuminemiaand hyperglobulinemiamay be present.

Erythrocyte sedimentation rateis usually raised.

Tuberculin skin test

Two tests are available: the Mantoux and Heaf tests.

Mantoux skin test

Image:Mantoux test.jpg

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 testare not recommended.

See: Mantoux testfor 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 testis 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

• 0-4 mm induration (Heaf 0-1)
• 5-14 mm induration (Heaf 2)
• >15 mm induration (Heaf 3-4)

Classification of tuberculin reaction

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

• 5mm or more is positive in
  • HIV-positive person
  • Recent contacts of TB case
  • Persons with nodular or fibrotic changes on CXR consistent with old healed TB
  • Patients with organ transplants and other immunosuppressed patients

• 10mm or more is positive in
  • Recent arrivals (less than 5 years) from high-prevalent countries
  • Injection drug users
  • Residents and employees of high-risk congregate settings (e.g., prisons, nursing homes, hospitals, homeless shelters, etc.)
  • Mycobacteriology lab personnel
  • Persons with clinical conditions that place them at high risk (e.g., diabetes, prolonged corticosteroidtherapy, leukemia, end-stage renal disease, chronic malabsorptionsyndromes, low body weight, etc)
  • Children less than 4 years of age, or children and adolescents exposed to adults in high-risk categories

• 15mm or more is positive in
  • Persons with no known risk factors for TB
  • (Note: Targeted skin testing programs should only be conducted among high-risk groups)

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

BCG vaccine and tuberculin skin test

Tuberculin skin testing is not contraindicated for BCG-vaccinated persons.

Latent TB infection (LTBI) diagnosis and treatment for LTBI is considered for any BCG-vaccinated person whose skin test is 10 mm or greater, if any of these circumstances are present:

• Was contact of another person with infectious TB
• Was born or has resided in a high TB prevalence country
• Is continually exposed to populations where TB prevalence is high.

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-rayor 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 Serviceshas an additional TB classification (Class A, B1, or B2) for immigrantsand refugeesdeveloped 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 classificationfor more details.

References

• Medical Examination of Aliens (Refugees and Immigrants) - Division of Global Migration and Quarantine, CDC (website).
• Targeted Tuberculin Testing and Treatment of Latent Tuberculosis Infection 2000 ATS/CDC (fulltext,PDF format) (Updates2001-2003).
• Lalvani A. ELISPOT Spotting latent infection: the path to better tuberculosis control. Thorax. 2003 Nov;58(11):916-8. Editorial. PMID 14586040

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It uses material from the http://en.wikipedia.org/wiki/Tuberculosis+diagnosis Wikipedia article Tuberculosis diagnosis.