Different concentrations and volumes of p-phenylenediamine in pet. (equivalent doses) are associated with similar patch test outcomes: a pilot study

SUMMARY

Background

Concern about causing active sensitization when patch testing is performed with p-phenylenediamine (PPD) 1% pet. has led to a recommendation to use PPD 0.3% pet. as a potentially safer preparation. However, the dose per area of allergen delivered, and hence the risk of active sensitization, depend on the amount dispensed into the patch test chamber, which can vary widely.

Objective

To evaluate whether patch testing with equivalent doses of different concentrations of PPD in pet. is associated with similar outcomes.

Methods

Seventeen known PPD-sensitive subjects were patch tested with different volumes and concentrations of PPD in pet. that deliver the same allergen dose per unit area (6 mg of PPD 1% pet. and 20 mg of PPD 0.3% pet. in Finn Chambers®, both equivalent to ∼ 0.09 mg/cm²).

Results

Eleven patients (65%) had positive reactions to both doses; 4 patients (24%) had negative results [percentage agreement of 88% (15/17)]. One patient each had a positive reaction to only one dose.

Conclusions

The 88% concordance suggests that dose per unit area is more important in determining reactions to allergens than the excipient volume dispensed. Patch testing with a smaller volume of 1% PPD may be a reasonable alternative to testing with 20 mg of 0.3% PPD.