Diagnosis of Tuberculosis

By  , Expert Content
Feb 06, 2012

Tuberculosis is a common infectious disease, which kills millions of people every year globally. The gold standard to diagnose TB is culture of the bacteria from sputum or any other sample, but it takes weeks to culture the bacteria and it may not be positive in many cases (even if they have TB). TB is usually diagnosed using a combination of skin, blood and imaging tests.

Mantoux test: It a simple skin test, which is often done in a person suspected of having TB. The test uses a small amount of purified protein derivative (PPD) tuberculin, which is injected into the forearm. After 48 to 72 hours, the injection site is checked for a reaction. In people, who have TB, a small hard and raised red bump develops at the injection site to indicate a positive test for TB.

Chest x-rays:
The chest X-ray is the most important test if you have TB. If there are changes that are related to TB in your chest x-ray, a sample of sputum will be sent for testing (microscopic examination and culture) in the lab.

Computer tomography (CT) scan: It may be done to diagnose TB. It is a painless and non-invasive test, which takes a series of detailed pictures of different parts of the body that is being examined. A radiologist can see the images and diagnose if there is an abnormality in the lung that is suggestive of TB infection. CT scan of other parts such as the brain, kidney or abdomen may be done if TB infection is suspected in these organs. A CT scan can be more informative than a chest X-ray to diagnose TB.

Sputum testing:
Sputum testing for tubercular bacilli is a confirmatory test for TB. If you cough sputum (the mucus you cough up) or can be induced, it may be sent for testing. The test, however, is positive in just about 30% of people with active disease. Apart from sputum, other bodily secretions such as from your stomach or lung fluid can be used as a sample for the culture of Mycobacteria to confirm the diagnosis. Culture of Mycobacterium tuberculosis takes about eight to 12 weeks. In some cases, the growth may be evident in one to three weeks, but may take eight to 12 weeks to be certain of the diagnosis.

QuantiFERON-TB Gold test:
This is a new test, which can help to diagnose TB. It is a blood test, which can help detect active and latent tuberculosis. It tests for the production of a substance called interferon-gamma (IFN-gamma) in response to TB bacteria by the immune cells.



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