GeneXpert technology

OBJECTIVES To evaluate the diagnostic validity of GeneXpert for the detection of Mycobacterium tuberculosis (MTB) in pericardial and pleural effusions samples. METHODS A cross sectional study was conducted at the Mycobacteriology Laboratory, Allama Iqbal Medical College, Lahore, Pakistan. A total of 286 (158 pleural and 128 pericardial fluids) samples were received from tuberculosis (TB) suspects between January 2014 and August 2016. Every sample was processed for Ziehl-Neelsen (Zn) smear, Lowenstein Jensen (LJ) culture, GeneXpert MTB/RIF assay according to standard protocols. Validity of GeneXpert assay for the detection of MTB was evaluated using LJ culture as gold standard. RESULTS Out of 286 effusions samples, MTB was isolated by LJ culture in 51 (17.8%) samples followed by GeneXpert in 43 (15%), and acid- fast bacilli (AFB)  was detected by Zn smear microscopy in 11 (3.8%) samples. GeneXpert showed high sensitivity (84.3%), specificity (100%), with positive predictive value (100%), and  negative predictive value (96.7%), while Zn smear showed sensitivity 18.3%, specificity 99.1%, positive predictive value 81.8%, and negative predictive value  85.4%. A strikingly high sensitivity of 72.2% was observed for pericardial fluid by GeneXpert. CONCLUSION GeneXpert assay is an innovative tool, for prompt detection of MTB and drug resistance. It is definitely an attractive point of care test, with high sensitivity and specificity along with turn around time of 2 hours, which facilitates timely diagnosis and appropriate management of TB pleuritis and pericarditis.