Contact Urticaria to Nickel: A Series of 11 Patients Who Were Prick Test Positive and Patch Test Negative to Nickel Sulfate 2.5% and 5.0.

BACKGROUND: Nickel is the most common allergen found by patch testing; however, not all cases of nickel allergy are type 4 (delayed) allergies. Contact urticaria (CU) to nickel (immediate reaction) has been reported; however, few seem to evaluate it as per a recent published survey of American Contact Dermatitis Society members.
OBJECTIVE: The aim of the study was to present a series of patients who had clinical histories suggestive of nickel allergy and yet were patch test negative but prick test positive to nickel, thus demonstrating CU.
METHODS: We reviewed the charts of 11 patients who were patch test negative but prick test positive.
RESULTS: All 11 patients demonstrated evidence of CU by prick testing (or closed chamber test in 1). None were patch test positive to nickel 2.5% or 5.0%. Four patients' histories mentioned reactions to various jewelry/earrings within minutes, whereas 2 histories mentioned reacting within a few hours. These histories are consistent with CU. Others (except 1 patient) recalled reacting to jewelry/earrings but did not recall a time frame.
CONCLUSIONS: Our series suggests that CU to nickel may be far more common than anticipated and should be evaluated with prick testing when patients' history suggests nickel allergy and yet they are patch test negative.