Many forms of EPTB are paucibacillary, and the diagnosis of EPTB is therefore challenging. Acid-fast bacilli (AFB) smear of biological specimens is often negative. Tuberculin skin testing (TST) and interferon-gamma release assays (IGRAs) are adjunctive diagnostic tools, at best. Constitutional symptoms associated with EPTB, (such as fever, weakness, and weight loss) may be infrequent and non-specific. In addition, EPTB is less common than pulmonary TB and may be less familiar to clinicians.
A high level of suspicion is important in evaluating a patient with presence of risk factors (for full details please refer to risk factor section). The firm diagnosis of TB requires culturing of Mycobacterium tuberculosis and is important for drug-susceptibility testing. Appropriate specimens are obtained and tested microbiologically and histologically. Although culture remains the diagnostic standard, it can take up to 8-10 weeks using a solid media, and in 10% to 15% of patients the diagnosis of TB is based on clinical grounds. Delays in diagnosis and initiation of therapy are associated with increased mortality.
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