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1.2.1. Justification
Based on available evidence, the WHO GDG panel concluded that the diagnostic accuracy of TBSTs is similar to that of IGRAs and greater than that of the TST. The GDG panel expressed concerns about the certainty (quality) of evidence in many areas and the lack of longitudinal studies that include impact on people affected by important outcomes of TB. The risk of bias was primarily from non-blinded studies, and the quantity and quality of evidence varied among the different tests. For two of the three tests (Diaskintest and C-TST) evaluated during the GDG meeting, evidence on specificity was generated in high TB burden settings; therefore, additional analysis considered the concordance in specificity with existing WHO-recommended IGRAs.
No safety concerns were identified for the class of tests; however, evaluation and approval by the competent regulatory agencies for the individual products are essential before introduction of these in vivo tests. Data on cost and cost–effectiveness were limited. Cost–effectiveness modelling calibrated to three countries (Brazil, South Africa and the United Kingdom of Great Britain and Northern Ireland [United Kingdom]) was commissioned to inform the GDG meeting. It was found that in Brazil and South Africa, use of TBSTs would be cost saving compared with both the TST and IGRAs; in the United Kingdom, it would be still cost saving compared with the TST but only cost-effective compared with IGRAs.
Qualitative evidence indicates that TBSTs are likely to improve health equity through the provision of a more accurate, low-cost test for resource-limited settings where the TST is already in use. It was suggested that TBSTs were perceived to have greater accuracy than the TST and were considered desirable because they avoid the negative consequences of false positive results. Finally, qualitative evidence supports the feasibility of using TBSTs in settings where the TST is already in use, because the required resourcing and training are already in place.
All three evaluated TBSTs have the potential to be used for the detection of TB infection and are recommended.
1.2.2. Subpopulations
Although the data were limited, based on the available evidence, the GDG members supported extrapolation of the recommendation for the following populations:
- People with HIV;
- children and adolescents aged under 18 years; and
- people who have been vaccinated with BCG.
For all the above-mentioned subpopulations, TBSTs are recommended.
Testing for TB infection is not a precondition for initiating TPT among and children under 5 years of age who are household contacts of people with active TB. Nevertheless, testing for TB infection increases the certainty that individuals will benefit from TPT.