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- 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.
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
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.
Abreugraphy
A variant of the chest X-Ray, abreugraphy (from the name of its inventor, Dr. Manuel Dias de Abreu) was a small radiographic image, also called miniature mass radiography (MMR) or miniature chest radiograph. Though its resolution is limited (it doesn't allow the diagnosis of lung cancer, for example) it is sufficiently accurate for diagnosis of tuberculosis.
Much less expensive than traditional X-Ray, MMR was quickly adopted and extensively utilized in some countries, in the 1950s. For example, in Brazil and in Japan, tuberculosis prevention laws went into effect, obligating ca. 60% of the population to undergo MMR screening.
The procedure went out of favor, as the incidence of tuberculosis dramatically decreased, but is still used in certain situations, such as the screening of prisioners and immigration applicants.
Laboratory
Mycobacterium tuberculosis produces the antigens early secretory antigen target 6 (ESAT-6) and culture filtrate protein 10 (CFP-10). These antigens are not present in non-tuberculous mycobacteria, nor in BCG vaccine.
The blood tests QuantiFERON-TB Gold and T-SPOT.TB use these antigens to detect people with tuberculosis. Lymphocytes from the patient's blood are cultured with the antigens. If the patient has been exposed to tuberculosis before, T lymphocytes produce interferon γ in response. The test then uses ELISA to detect the interferon γ.
QuantiFERON-TB Gold quantifies the amount of interferon γ when whole blood is exposed to the antigens. T-SPOT.TB counts the number of activated T lymphocytes. These tests are called interferon γ tests and are not equivalent.
Guidelines for 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 available in the UK that may replace the skin test for diagnosis. PMID 14586040
Microbiological studies
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 acid-fast. 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.
Full blood count
Although a full blood count is never diagnostic, normocytic anemia and lymphopenia are common. Neutrophilia is rarely found.
Urea and electrolytes are usually normal, although hypocalcemia and hyponatremia are possible in tuberculous meningoencephalitis due to SIADHS. In advanced disease, hypoalbuminemia and hyperglobulinemia may be present.
Erythrocyte sedimentation rate is usually raised.
Tuberculin skin test
Two tests are available: the Mantoux and Heaf tests.
Mantoux skin test
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
- 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 5-15 mm (depending upon the person's risk factors) to 10 Mantoux units is considered a positive result, indicating TB infection.
- 5 mm 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
- 10 mm 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 corticosteroid therapy, leukemia, end-stage renal disease, chronic malabsorption syndromes, low body weight, etc)
- Children less than 4 years of age, or children and adolescents exposed to adults in high-risk categories
- 15 mm 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 10 mm 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-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
- 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) (Updates 2001-2003).
- Lalvani A. ELISPOT Spotting latent infection: the path to better tuberculosis control. Thorax. 2003 Nov;58(11):916-8. Editorial. PMID 14586040
"Tuberculosis diagnosis"