Why might i need a tuberculin skin test done twice?

TB test: If you were in close contact with an active case of tuberculosis and tested borderline or indeterminate, a second test maybe necessary in 8-10 weeks to completely rule out the disease. Since the test has limitations, screening for tuberculosis with igras or interferon-gamma release assays, has been recommended by the cdc especially for those who received bcg, are homeless, and history drug abuse.