Diagnostic accuracy of Gene Xpert MTB/RIF and AFB Smear Compared to Culture for the Detection of Tuberculosis using Bronchio-Alveolar Lavage (BAL) Fluid

Raza Ullah, Imranullah Khan, Muhammad Shah Fahad, Muhammad Irfan, Kashif Aziz

Abstract


BAckground: A disease caused by Mycobacterium, known as Tuberculosis (TB) is a global health problem, in a developing country like Pakistan. The widely available medical therapy has a high cure rate but the main issue with TB is the need for the rapid diagnostic test with high accuracy to commence an early treatment.

Objective: This study was done to assess the diagnostic accuracy of GeneXpert and acid-fast bacilli (AFB) smear in comparison to the culture to detect TB using a Broncho alveolar lavage (BAL) fluid.

Methodology: A prospective observational study was carried out in the Department of Pulmonology, Rehman Medical Institute (RMI) Peshawar, from January 2018 to December 2019. A standardized proforma was used for data collection. Demographic, laboratory findings, clinical and radiological features were recorded and subsequently entered Statistical Package for Social Sciences (SPSS). After completing data entry, the statistical analysis was performed using SPSS version 23.0. Frequency of AFB smears, GeneXpert assay and mycobacterial cultures were calculated by percentages. Sensitivity, specificity and predictive values were calculated with 95% class intervals (CIs). A P < 0.05 was considered statistically significant.

Results: A total of 88 patients fulfilling the inclusion criteria were included in the study. The mean age of the patients was 49.5±18.01. About 59 patients (67%) were males while the rest were female patients. The most common symptoms included fever (78.4%), weight loss (71.6%), cough (64.8%), anorexia (43.2%) and breathlessness (29.5%). Out of 88 patients who were tuberculosis suspect, 73 (82.9%) cases were confirmed as pulmonary tuberculosis on mycobacterial cultures which was taken as a gold standard. On GeneXpert assay 72 (81.8%) cases and on AFB (BAL) smear only 52 (59.1%) were positive for MTB.

Conclusion: GeneXpert had a high sensitivity than AFB smear to detect Mycobacterium tuberculosis and rifampicin resistance (with high sensitivity and specificity), in those cases of pulmonary tuberculosis who have either smear negative or sputum scarce disease. This test has the advantages of being inexpensive, requires less manpower and gives results on the same day.


Keywords


Gene Xpert; MTB; Pulmonary TB; Sensitivity; Broncho alveolar lavage; Cultures

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