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A tuberculosis chest x-ray is a diagnostic procedure used to detect the presence of tuberculosis in the lungs. This procedure is used as a secondary screening method in patients who have had a positive skin test and in patients who are at high risk for tuberculosis infection but have not had a positive skin test. It is more accurate than a simple skin test but still not absolutely definitive, as tuberculosis can be a very difficult disease to accurately diagnose.
Tuberculosis is a very common variety of bacterial infection and is endemic throughout much of the developing world. In tuberculosis, bacteria typically invade and colonize the lungs where they begin to slowly grow and establish themselves, causing damage over time to lung tissue. It is somewhat unusual in that it grows very slowly under normal circumstances and, in a majority cases, can be suppressed, though not completely defeated, by a healthy human immune system.
The usual test to determine if a person has been exposed to tuberculosis is a minor skin prick test. In this test, tuberculin is injected into the body. If a patient has previously been exposed to tuberculosis or vaccinated against it, they will usually react to this agent, whereas patients who have not been exposed will usually have no reaction. The test is not universally accurate, however, and is especially unreliable among patients with compromised immune systems, who are among the most vulnerable to a tuberculosis infection.
In ambiguous cases or when dealing with an individual with a suppressed immune system, a tuberculosis chest x-ray is used to improve the accuracy of tuberculosis testing. When fighting off tuberculosis, the immune system encases the slow-growing bacteria in small bubbles within the lungs. The bubbles are normally visible on an x-ray. A tuberculosis chest x-ray will also reveal a larger and more virulent tuberculosis infection that has begun to spread through lung tissue.
A diagnostic tuberculosis chest x-ray is usually more accurate than a skin test but is not always able to diagnose an infection accurately. Blood tests may also be used as part of the diagnostic process for further accuracy. Once a tuberculosis chest x-ray or other test has shown that a patient is likely to have an active and growing infection, that infection will need to be sampled so that an effective mixture of antibiotics can be selected to treat the disease.