The role of chest X-ray in the diagnosis of bacteriologically confirmed pulmonary tuberculosis in hospitalised Xpert MTB/RIF-negative patients

Introduction The role of a chest X-ray (CXR) to diagnose active tuberculosis (TB) in symptomatic patients who have a negative Xpert MTB/RIF (Xpert) test result is unclear. This study aimed to assess the performance of CXR and the value of CXR findings for a prediction tool to identify cases of active pulmonary TB among symptomatic, Xpert-negative hospitalised patients.

Methods Xpert-negative patients hospitalised between January and July 2019 at Jimma University Medical Center in Ethiopia were assessed by mycobacterial culture and CXR. CXR was interpreted by a clinician for clinical decision making and by a radiologist for research purposes. Using bacteriological confirmation as the reference standard, the performance of CXR to diagnose active TB was assessed by the area under the receiver operating characteristic (AUC) curve, predictors of active TB were identified using bivariate and multivariate logistic regression analyses.

Results Of 247 Xpert-negative patients, 38% and 40% were classified as suggestive of TB by clinician and radiologist, respectively. Of the 39 (15.8%) bacteriologically confirmed cases, 69% and 79% were classified as having CXR findings suggestive of TB by clinician or radiologist, respectively. While there was a strong association between bacteriologically confirmed TB and CXR classified by clinician as suggestive of TB (aOR 2.7, 95% CI: 1.2–6.6), CXR with signs typical of TB (aOR 5.3, 95% CI: 2.1–14.4) or compatible with TB (aOR 5.1, 95% CI: 1.3–20.0), the positive predictive value of the CXR was low (27% and 34% for classification by clinician and radiologist, respectively). The addition of CXR findings by clinician or radiologist to clinical characteristics did not improve the performance of the prediction tool, with similar risk classification distribution, AUCs and negative and positive prediction values.

Conclusion Despite the strong association between CXR findings and active TB among hospitalised Xpert negative individuals, CXR findings did not improve the performance of a risk prediction tool based solely on clinical symptoms. Countries with a high TB/HIV burden should urgently replace Xpert by the more sensitive Xpert ultra assay to improve the diagnosis of active TB.