Box 19. Recommendation.

T-cell in vitro assays can be used as an optional complementary testing method for delayed reactions such as MPE, FDE, AGEP, and DRESS if other tests are negative or contraindicated (e.g. in patients following DRESS).

They should be performed 14 days at the earliest following the reaction, but then as soon as possible, even though diagnostically helpful results can still be obtained even after many years.

If possible, T-cell testing for SJS/TEN should be considered within 1 week following symptom onset.

The ELISpot assay can be an instrument to identify the triggering agent in severe drug reactions such as bullous reactions and DRESS/DIHS.