Diagnosis of TB Chest x-ray Acid-fast stain and culture Tuberculin skin test (TST) or interferon-gamma release assay (IGRA) When available, nucleic acid amplification test (NAAT) Pulmonary tuberculosis is often suspected based on one of the following: Chest x-rays taken while evaluating respiratory symptoms (cough lasting > 3 weeks, hemoptysis, chest pain, dyspnea), an unexplained illness, fever of unknown origin (FUO), or a positive tuberculin skin test (TST) IGRA done as a screening test or during contact investigation Suspicion for TB is higher in patients who have fever, cough lasting > 2 to 3 weeks, night sweats, weight loss, and / or lymphadenopathy and in patients with possible TB exposure (eg, via infectious family members, friends, or other contacts; institutional exposure; or travel to TB-endemic areas).