Abstract
RationaleChest radiography is sometimes the only method available for investigating patients with possible pulmonary tuberculosis (PTB) with negative sputum smears. However, interpretation of chest radiographs in this context lacks specificity for PTB, is subjective and is neither standardized nor reproducible. Efforts to improve the interpretation of chest radiography are warranted.ObjectivesTo develop a scoring system to aid the diagnosis of PTB, using features recorded with the Chest Radiograph Reading and Recording System (CRRS).MethodsChest radiographs of outpatients with possible PTB, recruited over 3 years at clinics in South Africa were read by two independent readers using the CRRS method. Multivariate analysis was used to identify features significantly associated with culture-positive PTB. These were weighted and used to generate a score.Results473 patients were included in the analysis. Large upper lobe opacities, cavities, unilateral pleural effusion and adenopathy were significantly associated with PTB, had high inter-reader reliability, and received 2, 2, 1 and 2 points, respectively in the final score. Using a cut-off of 2, scores below this threshold had a high negative predictive value (91.5%, 95%CI 87.1,94.7), but low positive predictive value (49.4%, 95%CI 42.9,55.9). Among the 382 TB suspects with negative sputum smears, 229 patients had scores <2; the score correctly ruled out active PTB in 214 of these patients (NPV 93.4%; 95%CI 89.4,96.3). The score had a suboptimal negative predictive value in HIV-infected patients (NPV 86.4, 95% CI 75,94).ConclusionsThe proposed scoring system is simple, and reliably ruled out active PTB in smear-negative HIV-uninfected patients, thus potentially reducing the need for further tests in high burden settings. Validation studies are now required.
Highlights
Despite the fact that tuberculosis (TB) is curable, it remains a major problem globally [1]
Among the 382 TB suspects with negative sputum smears, 229 patients had scores,2; the score correctly ruled out active pulmonary tuberculosis (PTB) in 214 of these patients (NPV 93.4%; 95%CI 89.4,96.3)
Smear microscopy has a sensitivity less than 50% among patients with active PTB who are co-infected with HIV [2], and in the HIV era, especially in some countries where more than 70% of patients are HIV-positive, additional methods are required for identifying patients requiring treatment [3]
Summary
Despite the fact that tuberculosis (TB) is curable, it remains a major problem globally [1]. While much work has been done to optimize sputum microscopy using strategies such as lightemitting diodes [2] and same-day diagnosis [4], in most clinical settings, the chest radiograph remains a central component of the diagnostic work-up, and has not been displaced by recently developed point of care tests, which are limited by both cost and availability [5,6]. In order to be helpful, chest radiographs require both observation and interpretation. Interpretation and utility can potentially be improved by a scoring system that makes the diagnostic decision less arbitrary by prescribing what constitutes a finding, and assigns weights to the features observed on the chest radiograph based on the likelihood of the association of such features with PTB
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