Published this month in a PLOS One article was a study intent on addressing the difficulty in expanding the use of GeneXpert MTB / RIF (Xpert) in low-income countries with highly constrained laboratory budgets. As a result of this study, tuberculosis experts concluded that an affordably priced and rapid “triage” or TB screening test could reduce overall diagnostic costs, and lead the way for additional use of Xpert. The result of this screening algorithm would be to focus the use of Xpert on most likely TB positive suspects. Combining these two technologies could provide similar TB detection performance and lower the overall diagnostic costs.
Over the past two years APVS has encouraged healthcare systems to adopt a layered diagnostic strategy that deploys TBDx™ as a screening technology. In this scenario, TBDx™ is used to screen or “triage” (identify) the most likely TB positive suspects. These positive cases would then be further tested using a molecular test.
Such a strategy aligns multiple objectives:
- It places the most affordable, rapid and effective diagnostic testing at the beginning, where the vast majority of suspects are tested and often found to be TB negative. These suspect cases do not require the more costly molecular test.
- It quickly identifies the sickest TB patients, removes them from further TB transmission potential, and starts their drug therapy immediately. In cases where the individual lives in a country with high cases of drug-resistant strains of TB, the patient receives a drug susceptibility test. Here, the added cost of a molecular test is well justified.
- It identifies the few hard-to-find “scanty” TB cases and employs a second molecular test for further case analysis. Again, this focuses the use of the molecular diagnostic on those cases most in need of such a test.
These are the precise objectives and recommendations presented by Dr. Nazir Ismail as a result of the TBDx evaluation in South Africa.
In a study entitled “Optimal Triage Test Characteristics to Improve the Cost-Effectiveness of the Xpert MTB / RIF Assay for TB Diagnosis: A Decision Analysis,” scientists leading the Xpert scale-up examined combinations of sensitivity, specificity and pricing that would be required to expand the use of Xpert on positive cases identified by the triage test. The hypothetical decision model outlined in the article was based on data adapted from studies in India, Uganda and South Africa. The study presents various scenarios, one where a triage test with sensitivity equal to Xpert, but with a specificity of 75% and a price less than US$5.00, could reduce the overall diagnostic costs from 34% to 42%. The study examined the relationship between the specificity and price of the triage test and lower levels of sensitivity.
Adding special emphasis to the study, which will provide helpful guidance for technology developers, are the authors themselves. Xpert was co-developed by the laboratory of Professor David Alland at the University of Medicine and Dentistry of New Jersey (UMDNJ). Dr. Jerrold Ellner is recognized internationally for his TB and HIV research efforts, publishing more than 250 peer-reviewed studies. Dr. Susan Dorman is an Associate Professor of Medicine at the Johns Hopkins University and has been involved in extensive operational evaluations of Xpert through the TB Clinical Diagnostic Research Consortium. Dr. Frank Cobelens is a professor of Epidemiology at the University of Amsterdam in The Netherlands, and has extensive experience in the evaluation of Xpert. Previously Dr. Cobelens participated in the WHO Strategic and Technical Advisory Group (STAG), the committee within WHO that reviews and recommends diagnostic technologies.
Acknowledgement of this possible diagnostic algorithm is encouraging news for APVS and its shareholders. It validates the screening and layering of diagnostics technologies that APVS has been promoting for the past two years. Lastly, it outlines likely performance characteristics and the per-test pricing needed for the triage test to be a viable option.
Based upon the evaluation performance in South Africa, the TBDx™ technology currently performs within the characteristics modeled in the study. Combining this performance with the TBDx™ per-slide cost that is well below the $5.00 threshold, positions TBDx™ as a very attractive screening technology. Coupling these characteristics with the ability of the technology to produce a result within 5 minutes, robotically process as many a 200 cases in one day (one of two product configurations) will lead to faster diagnosis, lower labor and training costs, and an increase in TB case detections.
The year ahead looks very favorable for the company.