Diagnosis

Skin testing is not advisable in people with a history of allergic reaction to TST or TBST. Allergic reactions to TST (PPD or equivalent), such as a generalized rash that occurs within the first 24 hours, are seen in less than 1% of recipients (26). If this has been well documented in the past, then it is wise to avoid repeating the test with the same tuberculin material. Currently, it is unclear whether use of an alternative tuberculin material would be safe.

TB infection tests should not be used for the diagnosis of pulmonary or extrapulmonary TB, nor should they be used for the diagnostic work-up of adults (including People with HIV) with presumed TB disease. TB infection tests should not be used for screening or to monitor the response to treatment for TB disease or TB infection.

TB infection testing may result in false negatives in individuals with certain viral illnesses (e.g. measles) or live virus vaccination (e.g. measles or mumps) within the preceding 30 days (23). This has been described with TST, but a similar effect with all TB infection tests is biologically plausible. Hence, it may be appropriate to delay the TB infection test for 30 days after infection or vaccination. Alternatively, a negative TB infection test may be repeated after 30 days.

If a prior positive TB infection test or TB treatment is documented, then repeat TB infection testing will not be useful and should not be done. Depending on the circumstances, the individual may be referred for further medical evaluation. However, if a prior positive result is self-reported and not documented, it is recommended to repeat the test, because studies have documented highly inaccurate self-reporting of prior skin test results (22).

This section sets out the various situations in which TB infection testing is not advised.

Testing for TB infection will be beneficial from an individual and a programmatic perspective if it identifies people who will benefit most from TPT. From a programmatic perspective, investments into capacity for TB infection testing will be justified if this results in greater efficacy and efficiency in the use of resources to provide TPT, increased acceptance and enhanced coverage. This will include not only the cost of drugs but also the human resources for medical evaluation, TPT initiation and follow-up.

Numerous studies have identified risk factors for TB disease in people with positive or negative tests for TB infection; these risk factors may be epidemiological (e.g. contacts), demographical (e.g. age) or clinical (e.g. HIV infection). These studies have recently been summarized, and pooled estimates of absolute and relative risks provided, in an aggregate data meta-analysis (6), and two large-scale individual patient data meta-analyses (4, 5). The risk of TB disease varies widely among those with different epidemiological or clinical risk factors.

The decision to test an individual for TB infection implies an intention to offer TPT. TB infection testing should therefore be reserved for populations in whom the risk of developing TB disease is high and who will benefit the most from TPT. Decisions to start TPT should always consider risk of adverse drug events, in addition to TB symptoms and the TB infection test result. Box 2.1 summarizes the groups WHO recommends should receive TPT, with testing not mandatory for groups 1–3. More detail can be found in Module 1 of the WHO operational handbook on TB (1).

This handbook is intended for use by TB and HIV programmes, and other experts involved in planning and implementing new or expanded programmes for TB infection testing. It is also intended for people involved in training, monitoring and supervision, and providers performing these tests. The annexes provide additional details, and educational materials about TB infection testing for providers and patients.