There are several tests available to diagnosis Tuberculosis. There are TB tests to find out if someone has drug resistant TB, are known as drug susceptibility tests. The development of TB disease is a two-stage process. In the first stage, known as latent TB, a person is infected with TB bacteria. In the second stage, known as active TB or TB disease, the bacteria have reproduced sufficiently to usually cause the person to have become sick. Some tests done by the general physicians are for latent TB, others are for active TB, and some are for both. A diagnosis of active TB disease can only be confirmed when there is definite evidence of TB bacteria in the person's body. Some of the TB tests, such as the skin test, look directly for TB bacteria. Others such as the chest X-ray look for the effect of the bacteria on the person suspected of having TB. The TB skin test involves injecting a small amount of fluid called tuberculin into the skin in the lower part of the arm. Then the person must return after 48 to 72 hours to have a trained health care worker look at their arm. The health care worker will look for a raised hard area or swelling, and if there is one then they will measure its size. Smear microscopy of sputum is often the first TB test to be used in countries with a high rate of TB infection.