D3.73 - Review of skin testing for delay hypersensitivity drug reactions, possible covariates involved in the results
Background
There is a lack of knowledge and standardization on the performance of dermal testing as a diagnostic tool for delayed hypersensitivity reactions (DHR) across different drugs and concentrations. We examined covariates predicting skin test positivity.
Method
We analyzed a retrospective cohort from 05/2014-02/2024 at a large tertiary care drug allergy clinic (VUMC), USA.
We identified 501 patients developed DHR (71% female, median age 54[IQR 37.31, 65.65]) where we performed 629 delayed skin tests (DT) of which 242 were patch tests (PT); 387 were delayed intradermal tests (dIDT), and 83 were both.
We examined the phenotype of the reaction, suspected culprit medication, time since the index reaction and the skin testing, and reagent concentration of testing.
Results
Overall, 74/629(11.8%) performed were positive. The rate of positive tests was higher in dIDT(50/387(13%)) than in PT(17/242(7%)).
The median time between the index reaction and the testing was 5.7 months. Time to testing for positive DT showed a shorter time of 4.6 months compared to negative DT of 5.9 months, in case of PT the difference was relevant (2.7 months compared to 5.9 months) but was not statistically significant (p=0.207).
The most common reaction associated with positive DT was DRESS(n=17/62(27%)), followed by AGEP(n=5/29(17.2%)), FDE(n=3/23)(13%)), and morbilliform drug eruption (MDE/MPE)(n=26/263 (9.8%)).
For vancomycin, no positive dIDT occurred <0.5 mg/mL and 5/6(83%) dIDT+ vancomycin DRESS cases carried HLA-32:01. Specific medications (cotrimoxazole, sulfasalazine, quinolones) were never positive regardless of phenotype.
No systemic reactions occurred.
Conclusion
DT is safe and specific but lacks sensitivity with dIDT being more sensitive than PT across all drugs and clinical phenotypes.
The performance of DT is dependent on the intradermal drug concentrations used, the specific medication tested and the clinical phenotype (sensitivity highest for DRESS>AGEP>FDE>MPE and lowest for SJS/TEN).
The highest non-irritating concentrations validated for immediate reactions have not been validated for delayed reactions and may lack sensitivity and 100% negative at non-irritating concentrations.
