The two screening tests done to diagnose tuberculosis are:
- Mantoux tuberculin skin test (TST)
- Blood test called interferon gamma release assay (IGRA)
In TST, the health care provider injects a small amount of substance called purified protein derivative (PPD) under the skin of the forearm. After two to three days, the doctor checks for the swelling at the injection site. The size of the raised skin determines the positive or negative result. In IGRA, the healthcare provider takes blood and sends the sample to the laboratory. Further tests done to determine whether the infection is active or the lungs are infected include laboratory tests done on sputum and lung fluid, chest X-ray and computed tomography scan.