COMPARATIVE EVALUATION OF CBNAAT WITH SMEAR MICROSCOPY, SYMPTOM SCREEN AND CHEST X-RAY FOR DIAGNOSIS OF PULMONARY TUBERCULOSIS

Anupam Kumar Singh, Dibyajyoti Karmakar, Rajendra Kumar Jha

Abstract


Context : CBNAAT-TB has emerged as an important diagnostic modality as more sensitive, rapid and accurate diagnostic modality for pulmonary Tuberculosis with fast detection of resistance.


Aim : Our Aim was to compare diagnostic accuracy of CBNAAT with commonly used modalities like smear microscopy, symptomatology and chest Xray for detection of pulmonary Tuberculosis and to enquire if it confers any diagnostic advantage in detection of smearnegative pulmonary TB.

Method. We screened all non –HIV patients present to TB- chest clinic for pulmonary TB.. We collected two sputum samples for microscopy using ZN stain , one sputum sample for CBNAAT and one sputum sample for BACTEC based culture in each patient . Using BACTEC culture positive as gold standard, we determined comparative sensitivity, specificity, Positive Predictive Value(PPV),Negative Predictive value(NPV), Positive Likelihood Ratio (PLR) and Negative Likelihood Ratio(NLR) of CBNAAT and sputum microscopy using SPSS 15.0 software and Bayesian sensitivity analysis was done with WINBUGS 1.3
Results : 598 patients were included in study .131/598 (34.8 %) patients were sputum culture positive and 19/131 were Rifampicin resistant. Overall sensitivity , specificity, PLR, NLR,PPV,NPV of CBNAAT and smear microscopy were [82.44(74.8 – 88.53), 98.29(96.65 - 99.26), 48.13, 0.18, 84.95 %, 89.70 %] and[ 60.3 (51.39 – 68.74), 97% (95.02 – 98.3),20.12, 0.41,75%,87.5% ] respectively . CBNAAT correctly picked up 29/52(55.76%) cases missed by smear microscopy. The Test accuracy as represented by AUROC ( Area under receiver operator characteristics) was significantly higher for CBNAAT compared to Sputum microscopy[0.904vs0.793,p=0.003)
Conclusion : CBNAAT-TB is more accurate, rapidly performed ,valid and important adjunct to sputum microscopy for detection of pulmonary tuberculosis.

Keywords


BACTEC, CBNAAT-TB, HIV

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