J Med Assoc Thai 2012; 95 (11):1396

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Sensitivity and Specificity of Real Time Polymerase Chain Reaction (RT-PCR) in Bronchial Washing for Diagnostic Pulmonary Tuberculosis at Maharat Nakhorn Ratchasima Hospital
Kheawon N Mail, Chuang-ngam S , Mitsoongneun S , Peam-am J , Visalsawadi J

Objective:To study sensitivity and specificity of real time polymerase chain reaction (RT-PCR) in bronchial washing for diagnostic pulmonary tuberculosis at Maharat Nakhorn Ratchasima Hospital.

Material and Method: A retrospective study of performed bronchial washing (BW) specimens for RT-PCR TB, AFB stain, and culture TB by conventional technique from 430 patients who had undergone bronchoscopic examination due to symptomatic abnormal CXR or Chest-CT with sputum samples negative or no sputum for AFB by the authors between December 1, 2008 and September 31, 2011. TB culture was gold standard in category A. Final diagnoses was confirmed with microbiological, clinicopathological finding and response to anti-TB treatment in category B. They were analyzed to study sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), positive and negative likelihood ratios of BW RT-PCR TB on diagnostic tool for detecting pulmonary TB. Statistical analysis of the data was described as percentage.

Results: Four hundred thirty patients were included in the presented study. Age range, sex, hemoptysis, smoking, CXR, and bronchoscope finding were not significant different between pulmonary TB and not pulmonary TB. The sensitivity, specificity, PPV, NPV, positive and likelihood ratios of bronchial washing for PCR-TB when applied to category A for diagnosing smear-negative pulmonary TB were 65.7%, 90.4%, 37.7%, 96.7%, 6.8, and 0.37 respectively. Category B were 43.2%, 93.3%, 62.3%, 86.4%, 6.4, and 0.6 respectively. After combination with BW AFB stain (bAFB), sensitivity was higher but specificity was less in both categories.

Conclusion: The low sensitivity of RT-PCR method might be low prevalence of active pulmonary TB in cases of the presented, the type of transfer and duration time (all of them were sent to a laboratory outside the hospital), the DNA extraction procedure, primer, the concentration of bronchial washing for DNA amplified, DNA extraction, and reproducible technique. However, BW RT-PCR should be done in a highly suspicious case due to rapid detection. False positive should be concerned in case of treated or old lesion from pulmonary TB.

Keywords: Bronchial washing, PCR-TB, Sensitivity, Specificity, IS6110

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