When a Doctor Performs a Mantaux Skin Test to Determine

When a doctor performs a Mantaux skin test to determine whether a patient has tuberculosis (TB), she exposes the patient to small amounts of protein from the microorganism that causes TB. The doctor reads the reaction to these proteins a few days later. If the patient has had previous TB antigen exposure (and infection), he or she will develop localized swelling at the site where the proteins were injected. The presence of swelling and the amount of swelling are observed and measured to determine whether the test is positive. Explain why this test measures a secondary (versus primary) exposure to antigens. Which aspects of this test demonstrate secondary exposure?

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The PPD test measures secondary exposure...

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