Human tuberculosis is passed by airborne transmission from person to person. Active TB and latent TB are not the same. Active TB is highly infectious with symptoms. Latent TB is not infectious and is without symptoms although can develop in people whose immunosuppressed status or clinical circumstances are altered. People with both active and latent TB will test positive. Patients with latent infection would be considered at risk of developing disease – and a standard treatment would therefore be undertaken. Detection of recent infection is the aim of TB screening and the goal of TB elimination. TB disease can occur in blood, lymph glands, brain, spine, kidneys and other organs but it usually occurs in the lungs. TB is endemic, with one third of the world’s population being infected with TB, and 8 million developing active TB every year. Resurgence of TB more recently in this country is a result of migration, travel (particularly to developing countries) urbanization and a number of other social factors.
To date, diagnosis has been made by staining, culture (6 weeks) or DNA detection of TB organisms from sputum (too expensive). Chest X-rays can also detect active TB of the lungs. Non-pulmonary TB infection is more difficult to diagnose.
A highly specific and sensitive test to detect active or latent TB is now available - QuantiFERON TB Gold - and provides a YES/NO result to Mycobacterium tuberculosis within 3-4 days from receipt of sample. This test replaces the Heaf/Tine/ Mantoux skin test. Sampling must be taken using specific vacutainer tubes and these can be supplied by Mullhaven Medical Laboratory. No special handling or refrigeration is needed for these tubes once the sample has been taken, but tubes must reach the laboratory for incubation and processing within 16 hours of drawing the sample.
The cost of the test is £64
Positive results may be the result of active or latent TB. Other specific tests would be indicated with positive results to determine whether this is a latent or active TB infection.
