Which test is used to determine prior exposure to tuberculosis?

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Assessing prior exposure to TB relies on detecting immune sensitization to TB antigens. The Mantoux test uses purified protein derivative injected under the skin; if you’ve been exposed before, your T cells remember TB and mount a delayed-type hypersensitivity reaction, causing a noticeable induration within about 48 to 72 hours. The size of that induration reflects prior exposure or infection, making this test the classic way to determine whether someone has been exposed to TB in the past.

Chest X-ray looks for current or past disease changes in the lungs, not just exposure. Sputum smear identifies active bacteria in the respiratory tract, indicating active disease rather than prior exposure. Interferon-gamma release assays can also indicate prior exposure or latent infection, but the Mantoux test is the standard tool for initially assessing past exposure.