Diagnosis of Tuberculosis
Clinically a person with latent TB will not have any symptoms.
A person with active TB will have a
- History of chronic coughing for more than a few weeks,
Not all persons will have all of the symptoms. If a person has one or more of the symptoms and has any history of contact with anyone suffering from TB or has visited any place where TB is common, he or she needs to be sent for diagnostic investigations. This is for the safety of the person and also to prevent the spread of the infection to all other people surrounding him or her.
Given below are some of the investigations that are commonly done to diagnose TB.
Skin Test
The skin test commonly used for testing for TB is the Mantoux test. It is also called the tuberculin sensitivity test or Purified Protein Derivative (PPD) test. It is the screening test for TB.
It is one of the inexpensive, portable and hassle free test making it very popular especially when the testing has to be carried out at remote places.
The testing material used is a TB antigen, Purified Protein Derivative (PPD). For this test, a standard dose of 5 Tuberculin units (0.1 mL) is injected intradermally and the area of injection is marked on the skin. After 48-72 hours the induration (bump) is measured. The size of the induration gives an idea of TB infection taking into consideration the risk factors of the person for TB.
The interpretation of the test is as follows.
Bump of 5 mm or greater is seen in persons
- with weakened immune systems, such as those with HIV/AIDS,
- who have been exposed to persons with active TB,
- with fibrotic changes on chest X-rays/scans that are consistent with an old TB infection,
- with organ transplants and other immunosuppressed patients (receiving the equivalent of >15 mg/day of prednisone for >1 month).
Bump of 10 mm or greater is seen in persons
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Arriving from a foreign country with a high number of TB patients,
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Who use injectable drugs,
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Who live or work in high-risk environments, such as cities and crowded areas
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Who work in laboratories, especially mycobacteriology
- Children under the age of 4 years
- Children and adolescents exposed to adults in high-risk environments.
Heaf test is another skin test, which was performed in the UK until 2005 after which Mantoux test has been adopted.
QuantiFERON-TB Gold
QuantiFERON-TB Gold is a recently approved test in USA, Europe and Japan. It provides equal if not more sensitivity as the Mantoux test, but is faster and the results are made available before 24 h and does not require a second visit like the Mantoux test.1 Also, it is a laboratory-based test and removes the error of recording and judgement as the measurement of the induration in the Mantoux test.
Chest X- ray
If the screening test gives a positive result, a chest X-ray is taken to confirm the lung findings.
Sputum Examination
Sputum is examined microscopically after appropriate staining to visualize the bacteria.
Next page: HIV and TB
Written by: Healthplus24 team
Date last updated: July 12, 2011