This invention relates to a test for detecting a Mycobacterium tuberculosis (tuberculosis or TB) infection in a patient or subject, specifically a diagnostic test, including a breath test, whereby patients are provided a small dose of an isotopically labeled TB drug, Isoniazid (INH) orally or directly to the lungs of the patient or subject. If TB is present, a TB enzyme mycobacterial peroxidase KatG oxidizes the INH; and KatG specific metabolites, in particular, isotopically labeled nitric oxide (NO), nitrites, nitrates, carbon monoxide (CO) or carbon dioxide converted from carbon monoxide of INH cleavage are measured. Other embodiments relate to a diagnostic breath test for detecting TB utilizing isotopically labeled urea (preferably, carbon-13 labeled urea), alone or in combination with isotopically labeled isoniazid (preferably, nitrogen-15 labeled isoniazid), wherein M. tuberculosis organism, if present in the patient or subject's lungs (or other tissues), will metabolize the isotopically labeled urea to isotopically labeled carbon dioxide (CO2) such that a determination of the residence of M. tuberculosis, including residence of an isoniazid resistant strain of M. tuberculosis, may be made.