Interferon Test

Discovered in 1882, tuberculosis (TB) is a potentially lethal infectious disease with severe complications. While its eradication in developed countries is substantial, TB is still contributing to morbidity and mortality in many parts of the world. Caused by the bacterium Mycobacterium tuberculosis, this disease primarily affects the lungs, resulting in decreased breathing capacity. Most individuals who contract an infection with TB will eliminate or contain the infection, resulting in latency. Transmission occurs through respiratory droplets from individuals with active disease. Reactivation of latent disease causes the resurgence of symptoms and the spread of the disease. There are currently 2 testing methods for identifying latent tuberculosis infection: the tuberculin skin test (TST) and the interferon-gamma release assay (IGRA). IGRA tests diagnose tuberculosis infection by either calculating the concentration of interferon-γ generated ex vivo by the patient's immune cells or by counting the total number of interferon-γ-secreting lymphocytes. The TST is performed by injecting a small amount of tuberculin purified protein derivative fluid subcutaneously into the forearm. Induration is measured 48 to 72 hours post-injection. The size of induration and the patient's risk factors together determine the test results. Conversely, the diagnosis of active TB is clinical, with confirmatory testing through sputum culture analysis.