Diagnosis
INITIAL TESTING
A common test used to diagnose a TB infection is a simple skin test called the Mantoux test (TB Skin Test).
In this test, a small amount of a substance called PPD tuberculin is injected into the skin of the inside forearm. The doctor would then examine the arm within 48 to 72 hours and check for a reaction to the injected material. The test is diagnosed as positive or negative depending on the response. A positive response is usually shown by a hard, raised bump at the injection site which indicates a TB infection.
Mantoux Skin Test. Image courtesy of en.wikipedia.org/wiki/File:Mantoux_tuberculin_skin_test.jpg. As work of the U.S federal government, the image is in the public domain and copyright free.
A blood test can also be used to detect the presence of TB bacteria. However it is not widely available yet.
FURTHER TESTING
If the results of a TB test are positive, further tests are needed to determine whether the TB bacteria is active:
These tests are:
Chest X-ray - If a patient had a positive skin test response, the doctor would perform a chest X-ray. If it is just an infection then the X-ray would show white spots where the immune system has walled off the Tuberculosis bacteria. However if the patient has active TB it could show a nodule or large air space in the lungs.
Chest X ray diagnosing active TB. Image courtesy of en.wikipedia.org/wiki/File:Tuberculosis-x-ray-1.jpg. As work of the U.S. federal government this image is in the public domain and copyright free.
Culture tests - If the chest X-ray shows signs of active TB the doctor may extract a sample of the patient’s sputum (the mucus that gets coughed up) and the stomach secretions. The samples are then sent to a laboratory where they are cultured on a special medium that encourages the growth of bacteria. The bacteria that appear are then examined to see if they show any affect to the anti-TB drugs. If they do then they can be identified as active TB bacteria that has spread throughout the body and the doctor can use these results to provide the most appropriate drugs for the patient.
TB bacteria cultured from sputum. Image courtesy of en.wikipedia.org/wiki/File:TB_in_sputum.png. As work of the U.S. federal government this image is in the public domain and copyright free.