I've never heard of an Extra Gold blood test, but doing a bit of research, it's used in place of the old skin test for diagnosing tuberculosis... This is what I found on the Quest Diagnostics site:
"QuantiFERON-TB Gold Plus (QFT-Plus) is a whole-blood test or interferon-gamma release assay (IGRA) that can measure a person’s immune reactivity and aid in diagnosing Mycobacterium tuberculosis infection. It offers advantages over the conventional tuberculin skin test (TST) for diagnosing LTBI.4,5"
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