Evaluation of molecular diagnostic assays in comparison with acid fast staining for detection of tuberculosis in patients attending a tertiary care hospital, Uttarakhand.

Ishan Pandita; Shashikant N Tayade; Taruna G Shirodker; Ankit Khanduri

doi:10.37022/wjcmpr.v8i3.433

Authors

Ishan Pandita Department of Microbiology, Graphic Era Institute of Medical Sciences, Dehradun, Uttarakhand, India.
Shashikant N. Tayade Department of Microbiology, Graphic Era Institute of Medical Sciences, Dehradun, Uttarakhand, India.
Taruna G Shirodker Department of Microbiology, Graphic Era Institute of Medical Sciences, Dehradun, Uttarakhand, India.
Ankit Khanduri Department of Microbiology, Graphic Era Institute of Medical Sciences, Dehradun, Uttarakhand, India.

Abstract

Background: Acid-fast bacilli (AFB) microscopy has limited sensitivity at low bacillary burden. Cartridge-based nucleic acid amplification testing (CBNAAT) detects Mycobacterium tuberculosis (MTB) directly and provides rifampicin-resistance information.

Aim: To compare AFB microscopy with CBNAAT for TB detection in clinical specimens at a tertiary care hospital in Uttarakhand.

Materials and methods: This specimen-based cross-sectional study included 304 specimens from 3,160 specimens received for presumptive TB evaluation during December 2025 to August 2026. AFB microscopy and CBNAAT (GeneXpert MTB/RIF Ultra) were compared in specimens, where both results were available. Molecular-load and rifampicin-resistance results were analyzed among CBNAAT-detected specimens.

Results: Of 304 specimens, 217 (71.4%) were respiratory and rest 87 (28.6%) were non-respiratory. AFB stain was positive for 92 and negative for 163specimens. CBNAAT detected MTB in 301 specimens; 3 were not detected and were reported as NTM. Among 255 specimens with both results, 163 (63.9%) were AFB-negative/CBNAAT-detected. AFB positivity increased from 0/14 (Trace) to 37/39 (High) across molecular-load categories (P < 0.001). Rifampicin resistance was detected in 13/274 determinate results (4.7%).

Conclusion: CBNAAT detected MTB in many AFB-negative specimens, while AFB positivity increased with molecular load. These findings describe concordance and discordance in the studied specimen set rather than diagnostic accuracy.

Keywords:

Tuberculosis, AFB microscopy, CBNAAT, GeneXpert MTB/RIF Ultra, molecular load, rifampicin resistance

DOI

https://doi.org/10.37022/wjcmpr.v8i3.433

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