Diagnosis

A person with suspected pulmonary TB (TB of the lungs) may be asked to give a sputum sample (spitting phlegm into a small container).  This is examined to see if the bacterium causing tuberculosis are present.

Sputum positive means that the bacteria have been found in the sputum. 

Sputum negative means that no bacteria have been found.  This does not necessarily mean the person does not have TB, and other tests may be given.

Other tests which may be given include a skin test, chest x-ray or blood test, depending on the circumstances.

• A tuberculin skin test (TST) checks the immune system's response to TB bacteria and tells whether there has been previous contact with TB. It works by using a small needle to inject a liquid called Tuberculin into the top layers of the skin. A return visit to clinic is required a few days later to have the reaction read. The TST can only show that the person has TB infection, not whether they have active TB. A negative reaction to the TST does not exclude the diagnosis of TB, especially for patients with severe TB illness or infection with HIV. Equally, previous BCG vaccination or exposure to other environmental mycobacteria can cause a positive reaction.
• A chest x-ray will indicate any damage to the lungs. In pulmonary (lung) TB, abnormalities are often seen in the upper parts of the lungs. However, lesions may appear anywhere in the lungs and may differ in size, shape, density, and cavitation, especially in HIV-positive and other immunosuppressed persons. Chest x-rays can indicate but not confirm TB. Chest x-rays may be used to rule out the possibility of lung TB in a person who has a positive reaction to the tuberculin skin test and no symptoms of disease.
• Blood tests are a recent development in the diagnosis of TB and are slowly becoming more widely available. Like the skin test, the blood test will not show whether the person has active TB, but indicates TB infection. Blood tests do not require a return visit to clinic for the reaction to be read and are unlikely to show false negative or false positive reactions. There are currently two types of blood test technology, QuantiFERON and T-SPOT.TB.

In developed countries, diagnosis of TB is fully confirmed by a positive culture growth of the tuberculosis bacterium in a laboratory. Not all hospitals or diagnostic centres will have this facility in developing countries.

Very rarely, TB can affect other parts of the body such as the lymph nodes, bones/joints, abdomen, heart, kidney, brain, and skin.  Other tests such as biopsy may be used in these cases.