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Background <p>Smear-negative pulmonary tuberculosis remains a major diagnostic challenge due to the limited sensitivity of conventional microscopy. Rapid molecular diagnostics, particularly Xpert MTB/RIF, provide a valuable approach for early detection.</p> Objective <p>To evaluate the diagnostic accuracy of Xpert MTB/RIF assay in smear-negative pulmonary tuberculosis and to assess its agreement and discordance with mycobacterial culture (reference standard) and chest radiography.</p> Methods <p>This prospective cross-sectional study included 50 patients with clinical suspicion of pulmonary tuberculosis and negative sputum smear microscopy. All participants underwent Xpert MTB/RIF testing, mycobacterial culture on Lowenstein–Jensen medium, and chest radiography. Diagnostic performance measures, including sensitivity, specificity, predictive values, and agreement using Cohen’s kappa coefficient, were calculated.</p> Results <p>Xpert MTB/RIF detected <i>Mycobacterium tuberculosis</i> in 30/50 patients (60%), while culture was positive in 38/50 patients (76%). Compared with culture, Xpert MTB/RIF demonstrated a sensitivity of 76.3% (95% CI: 59.8–88.6) and a specificity of 91.7% (95% CI: 61.5–99.8). The positive predictive value and negative predictive value were 96.7% and 55.0%, respectively, with an overall diagnostic accuracy of 80.0%. Agreement between Xpert MTB/RIF and culture was moderate (Cohen’s kappa = 0.50), with an overall agreement of 80%. Chest radiography showed moderate agreement with both Xpert MTB/RIF (kappa = 0.576) and culture (kappa = 0.478). Discordant results included 9 false-negative and 1 false-positive Xpert MTB/RIF case.</p> Conclusion <p>Xpert MTB/RIF represents a rapid adjunctive diagnostic tool for smear-negative pulmonary tuberculosis, characterized by high specificity and moderate sensitivity. While useful as a rule-in test, negative results should be interpreted cautiously, particularly in paucibacillary disease. Integration with microbiological and radiological assessment may provide complementary diagnostic information in clinically suspected cases.</p>

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Diagnostic accuracy, agreement, and discordance of Xpert MTB/RIF compared with culture and chest radiography in smear-negative pulmonary tuberculosis

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月10日

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  • Ahmed F. Mady,
  • Naema Khodeir Aly,
  • Heba Elsayed Mabrouk Dabiza,
  • Fatma Mohamed Mohamed Kamel,
  • Niveen Mohammed Ahmed Ghoraba

摘要

Background

Smear-negative pulmonary tuberculosis remains a major diagnostic challenge due to the limited sensitivity of conventional microscopy. Rapid molecular diagnostics, particularly Xpert MTB/RIF, provide a valuable approach for early detection.

Objective

To evaluate the diagnostic accuracy of Xpert MTB/RIF assay in smear-negative pulmonary tuberculosis and to assess its agreement and discordance with mycobacterial culture (reference standard) and chest radiography.

Methods

This prospective cross-sectional study included 50 patients with clinical suspicion of pulmonary tuberculosis and negative sputum smear microscopy. All participants underwent Xpert MTB/RIF testing, mycobacterial culture on Lowenstein–Jensen medium, and chest radiography. Diagnostic performance measures, including sensitivity, specificity, predictive values, and agreement using Cohen’s kappa coefficient, were calculated.

Results

Xpert MTB/RIF detected Mycobacterium tuberculosis in 30/50 patients (60%), while culture was positive in 38/50 patients (76%). Compared with culture, Xpert MTB/RIF demonstrated a sensitivity of 76.3% (95% CI: 59.8–88.6) and a specificity of 91.7% (95% CI: 61.5–99.8). The positive predictive value and negative predictive value were 96.7% and 55.0%, respectively, with an overall diagnostic accuracy of 80.0%. Agreement between Xpert MTB/RIF and culture was moderate (Cohen’s kappa = 0.50), with an overall agreement of 80%. Chest radiography showed moderate agreement with both Xpert MTB/RIF (kappa = 0.576) and culture (kappa = 0.478). Discordant results included 9 false-negative and 1 false-positive Xpert MTB/RIF case.

Conclusion

Xpert MTB/RIF represents a rapid adjunctive diagnostic tool for smear-negative pulmonary tuberculosis, characterized by high specificity and moderate sensitivity. While useful as a rule-in test, negative results should be interpreted cautiously, particularly in paucibacillary disease. Integration with microbiological and radiological assessment may provide complementary diagnostic information in clinically suspected cases.