TB screening tools are designed to distinguish people with a higher probability of having TB disease from those with a low probability and can be assumed to be free of TB disease. They are not intended to provide a definitive diagnosis. In general, they need to be able to be implemented easily and relay results rapidly in order to be informative in a screening context. Screening tests need to be followed by a diagnostic test, offered as part of a comprehensive clinical evaluation, to confirm or rule out TB disease in individuals who screen positive.
The most desirable screening strategy would be one with a high total yield of true-positive cases of TB, few false positives, low NNS, low cost, a rapid and simple algorithm and high client acceptability. In practice, many of these factors tend to run in opposite directions, so a multifactorial analysis is needed to decide which screening tools and algorithms to use.
In 2014, WHO released a report summarizing the desirable characteristics, or target product profiles, of screening tests for detecting TB disease (67). The report highlighted that the minimal requirements for a target screening test would be an overall sensitivity of 90% and a specificity of 70% to detect pulmonary TB disease or rule it out in individuals being screened. Based on these benchmarks, an array of potential tools for screening for TB disease in different populations was considered by the GDG.