Background The grading of radiological severity in clinical trials in tuberculosis (TB) remains unstandardised. The aim of this study was to generate and validate a numerical score for grading chest x-ray (CXR) severity and predicting response to treatment in adults with smear-positive pulmonary TB.

Methods At a TB clinic in Papua, Indonesia, serial CXRs were performed at diagnosis, 2 and 6 months in 115 adults with smear-positive pulmonary TB. Radiographic findings predictive of 2-month sputum microscopy status were used to generate a score. The validity of the score was then assessed in a second data set of 139 comparable adults with TB, recruited 4 years later at the same site. Relationships between the CXR score and other measures of TB severity were examined.

Results The estimated proportion of lung affected and presence of cavitation, but not cavity size or other radiological findings, significantly predicted outcome and were combined to derive a score given by percentage of lung affected plus 40 if cavitation was present. As well as predicting 2-month outcome, scores were significantly associated with sputum smear grade at diagnosis (p<0.001), body mass index, lung function, haemoglobin, exercise tolerance and quality of life (p<0.02 for each). In the validation data set, baseline CXR score predicted 2-month smear status significantly more accurately than did the proportion of lung affected alone. In both data sets, CXR scores decreased over time (p<0.001).

Conclusion This simple, validated method for grading CXR severity in adults with smear-positive pulmonary TB correlates with baseline clinical and microbiological severity and response to treatment, and is suitable for use in clinical trials.