<s>[INST] 17 year old, male, 5"'4", 130 pounds, good health, had TST done and came out positive. The chest X-ray came out negative. Pt took BCG vaccination 15 years ago. Can the TST be false positive because pt took BCG before?  Can we do another test before start taking INH medication? [/INST] Hi,I appreciate your knowledge. Yes if pateint has taken BCG vaccine than tuberculin skin test that is TST can be false positive. And TST is not conformatory test for tuberculosis and treatment started only after TB confirmation by suitable methods like:- Chest x ray - Sputum AFB study- Gene expert if needed Clinical correlation also done before starting tuberculosis treatment.Hope your concern is solved. You can consult good pulmonologoist for examination and further work up accordingly. Let me know if I can assist you further.Regards,Dr. Parth Goswami </s>