<P> Clinical evaluation and additional tests (such as a chest radiograph, sputum smear, and culture) are needed to differentiate between a diagnosis of latent TB or active TB . </P> <P> Advantages of the test are: </P> <Ul> <Li> Requires a single patient visit to draw a blood sample . </Li> <Li> Results can be available within 24 hours . </Li> <Li> Does not boost responses measured by subsequent tests, which can happen with tuberculin skin tests (TST). </Li> <Li> Is not subject to reader bias that can occur with TST . </Li> <Li> Is not affected by prior BCG (bacille Calmette - Guérin) vaccination . </Li> </Ul> <Li> Requires a single patient visit to draw a blood sample . </Li>

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