Intradermal testing after negative skin prick testing for patients with high suspicion of allergy

Skin testing is a widely accepted method for identifying inhalant allergies. Intradermal (ID) testing is often performed after negative skin prick testing (SPT) when a practitioner has a high level of clinical suspicion for a particular allergen.

A retrospective chart review study was performed over a 5-year period in patients with negative SPT for airborne allergens who also underwent ID testing based on a high level of suspicion for clinical allergy.

Eighty-seven patients had negative SPT and went on to receive an average of 7 ID tests per patient. A total of 592 ID tests were performed after negative SPT. Of these, 20.8% (123/592) had a positive ID result with negative SPT. The allergens with the greatest percentage of positive ID results with negative SPTs were dog, cat, D. farinae, and D. pteronyssinus (33.3%, 34.3%, 39.4%, and 39.6%, respectively). The allergens least likely to test positive on ID testing after negative SPT were red maple, Cladosporium, and Alternaria (0%, 6.3%, and 6.5%, respectively).

Approximately 20% of all negative results on SPT will have a positive ID test, more likely for indoor allergens. If a high suspicion for allergy exists in a patient with a negative SPT result, it may be useful to proceed with ID testing. However, the clinical significance of a positive ID test after negative SPT still needs to be elucidated.