Sensitivity and Specificity of Real Time Polymerase Chain Reaction (RT-PCR) in Bronchial Washing for Diagnostic Pulmonary Tuberculosis at Maharat Nakhorn Ratchasima Hospital
Nabhathara Kheawon MD*, Suthanya Chuang-ngam RN*, Suparat Mitsoongneun RN*, Janisaya Peam-am RN*, Jarukorn Visalsawadi MSc**
Affiliation : * Division of Pulmonary and Critical, Department of Medicine, Maharat Nakhon Ratchasima Hospital, Nakhon Ratchasima, Thailand ** Division of Laboratory, Department of Medicine, Maharat Nakhorn Ratchasima Hospital, Nakhon Ratchasima, Thailand
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
