In places where TB is not prevalent, TB infection can be diagnosed using a skin test. To perform a skin test, a health care worker inserts a small needle filled with tuberculin (a protein found in TB bacteria) under the skin on the inside of the arm as shown in this Centers for Disease Control photograph. Two to three days later, the health care worker measures the amount of skin swelling around the test area. A large amount of swelling indicates that the person is infected with TB. Of course, since only 5 to 10 percent of people infected with TB develop the disease, a positive TB skin test does not mean that the person will get the disease.
In places where many people have TB (such as India, Moldova, and South Africa), doctors don’t usually use the skin test. In these areas, TB is diagnosed when it is symptomatic. Many people with TB in these countries are hospitalized, as is this patient at the Group of TB Hospitals in Mumbai, India.
To make a TB diagnosis, a health care worker will explore a person’s symptoms. Do they have a cough that they’ve had for more than three weeks? Do they cough up sputum? Is the sputum sometimes bloody? Do they have chest pain? Are they easily fatigued? Are they losing weight?
In this photo, Vishwakarma Ramcharita (Mumbai, India) tells health care workers that although he has finished his treatment, he still feels sick.
Health care workers also x-rays people’s lungs. TB most often affects the upper lobes of the lungs and can be seen on x-ray as numerous white, irregular areas against a dark background. In the developing world, many people do not have access to x-rays, making TB even more difficult to diagnose.
To make sure that the person really does have TB, the health care worker takes a sample of sputum or tissue (a biopsy) to examine. Samples—like the sputum samples inside the National Tuberculosis Lab in Chisinau, Moldova, shown in this photograph—are sent to a laboratory where they’re examined under a microscope to look for the TB bacteria. They are also placed on a special medium that allows the bacteria to grow and reproduce (a culture). The growth is then tested to see if it is actually Mycobacterium tuberculosis. Performing a culture can take quite a long time (from four to eight weeks) because the TB bacteria reproduce slowly.
In 2010, the World Health Organization (WHO) unveiled a much faster test for TB. The automated test machine analyzes saliva for TB in 100 minutes. It is hoped that the test will be made available at affordable prices to low- and middle-income countries where TB is problematic.