Association Between Cycle Threshold Value of Cartridge-Based Nucleic Acid Amplification Test and Clinical Severity of Pulmonary Tuberculosis: A Cross-sectional Study

Abstract

Introduction: Tuberculosis (TB) is a major global health problem caused by Mycobacterium tuberculosis (MTB). The National Tuberculosis Elimination Programme (NTEP) emphasises early diagnosis and treatment of TB cases. The Cartridge-Based Nucleic Acid Amplification Test (CBNAAT) is a semi-automated molecular assay that rapidly detects MTB Deoxyribonucleic Acid (DNA) and Rifampicin (RIF) resistance-associated mutations using Real-Time Polymerase Chain Reaction (RT-PCR). Aim: This cross-sectional study aims to assess the association between the Cycle Threshold (Ct) value of CBNAAT and the clinical severity of Pulmonary Tuberculosis (PTB). Materials and Methods: The study was conducted at the Department of Respiratory Medicine, Navodaya Medical College Hospital and Research Centre-Raichur, from January 2020 to July 2021. A sample size of 106 participants, aged ≥18 years and meeting the NTEP guidelines for presumptive PTB cases, were enrolled. Participants underwent chest radiography, sputum smear microscopy for Acid-Fast Bacilli (AFB), and CBNAAT testing. Clinical severity of PTB was categorised as mild, moderate, or severe using the Bandim TB score. Data was entered into Microsoft Excel 2017, and statistical analysis was performed using SPSS version 23. Descriptive statistics, frequencies, percentages, means, and standard deviations were calculated, and the chi-square test was utilised to assess associations between qualitative variables. Results: Among the participants, the majority (55.7%, n=59) had moderate clinical severity. Of these, 12.3% (n=13) had high CBNAAT Ct values, 20.8% (n=22) had medium Ct values, 11.3% (n=12) had low Ct values, and 11.3% (n=12) had very low Ct values. A total of 31.1% (n=33) had severe clinical severity, with 13.2% (n=6) having high Ct values, 12.3% (n=13) having medium Ct values, and 6.6% (n=7) each having low and very low Ct values. Additionally, 13.2% (n=14) had mild clinical severity, with 0.9% (n=1) having high Ct values, 3.8% (n=4) having medium Ct values, 5.7% (n=6) having low Ct values, and 2.8% (n=3) having very low Ct values. The chi-square value was 4.697, with a p-value of 0.58. Conclusion: There is no association between the Ct value of CBNAAT and the clinical severity of PTB.