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. 2015 Jul 27:5:12215.
doi: 10.1038/srep12215.

Automated chest-radiography as a triage for Xpert testing in resource-constrained settings: a prospective study of diagnostic accuracy and costs

R H H M Philipsen  1 , C I Sánchez  1 , P Maduskar  1 , J Melendez  1 , L Peters-Bax  2 , J G Peter  3 , R Dawson  3 , G Theron  3 , K Dheda  3 , B van Ginneken  1
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Automated chest-radiography as a triage for Xpert testing in resource-constrained settings: a prospective study of diagnostic accuracy and costs

R H H M Philipsen et al. Sci Rep. .

Abstract

Molecular tests hold great potential for tuberculosis (TB) diagnosis, but are costly, time consuming, and HIV-infected patients are often sputum scarce. Therefore, alternative approaches are needed. We evaluated automated digital chest radiography (ACR) as a rapid and cheap pre-screen test prior to Xpert MTB/RIF (Xpert). 388 suspected TB subjects underwent chest radiography, Xpert and sputum culture testing. Radiographs were analysed by computer software (CAD4TB) and specialist readers, and abnormality scores were allocated. A triage algorithm was simulated in which subjects with a score above a threshold underwent Xpert. We computed sensitivity, specificity, cost per screened subject (CSS), cost per notified TB case (CNTBC) and throughput for different diagnostic thresholds. 18.3% of subjects had culture positive TB. For Xpert alone, sensitivity was 78.9%, specificity 98.1%, CSS $13.09 and CNTBC $90.70. In a pre-screening setting where 40% of subjects would undergo Xpert, CSS decreased to $6.72 and CNTBC to $54.34, with eight TB cases missed and throughput increased from 45 to 113 patients/day. Specialists, on average, read 57% of radiographs as abnormal, reducing CSS ($8.95) and CNTBC ($64.84). ACR pre-screening could substantially reduce costs, and increase daily throughput with few TB cases missed. These data inform public health policy in resource-constrained settings.

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Figures

Figure 1
Figure 1. Two example CXRs with corresponding heatmaps.
(a) Culture negative CXR with an ACR score of 18. (b) Corresponding abnormality heatmap. (c) Culture positive CXR with a subtle abnormality visible on the CXR and picked up by the CAD4TB software resulting in an ACR score of 71. (d) Corresponding abnormality heatmap. ACR, automated chest radiography; CXR, chest X-ray.
Figure 2
Figure 2. Diagnostic algorithm proposed in this paper.
Subjects presenting at a TB screening unit start with a pre-screening ACR with a 1-minute computation time to determine whether follow-up Xpert test is needed. In the latter case, the Xpert test takes 2 hours to complete. ACR, automated chest radiography; TB, tuberculosis; Xpert, Xpert MTB/RIF.
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