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.