Added value of interferon-gamma release assays in screening for tuberculous infection in the Netherlands.

BACKGROUND

Interferon-gamma release assays (IGRAs) are reported to be more specific for the diagnosis of latent tuberculous infection (LTBI) than the tuberculin skin test (TST). The two-step procedure, TST followed by an IGRA, is reported to be cost-effective in high-income countries, but it requires more financial resources.

OBJECTIVE

To assess the added value of IGRA compared to TST alone in the Netherlands.

METHODS

Test results and background data on persons tested with an IGRA were recorded by the Public Municipal Health Services in a web-based database. The number of persons diagnosed with LTBI using different screening algorithms was calculated.

RESULTS

In those tested with an IGRA, at least 60% of persons who would have been diagnosed with LTBI based on TST alone had a negative IGRA. Among those with a TST reaction below the cut-off for the diagnosis of LTBI, 13% had a positive IGRA. For 41% of persons tested with an IGRA after TST, the IGRA influenced whether or not an LTBI diagnosis would be made.

CONCLUSION

With the IGRA as reference standard, a high proportion of persons in low-prevalence settings are treated unnecessarily for LTBI if tested with TST alone, while a small proportion eligible for preventive treatment are missed. Incremental costs of the two-step strategy seem to be balanced by the improved targeting of preventive treatment.