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

B A C K G R O UND: 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 costeffective
in high-income countries, but it requires more
financial resources.
OBJ E C T I V E : 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.
RESULT S : 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.