Variation in the amount of petrolatum preparation applied at patch testing.

The elicitation of a positive patch test reaction in a given individual depends upon the dose of the sensitizer applied, the patch test technique and the occlusion time. The dose is determined by the concentration and volume/amount of test preparation applied. If the same amount/volume of a test preparation is applied all the time with the same test technique (same area of skin) and occlusion time, it is appropriate to use concentration as a dose parameter. Most contact sensitizers are incorporated in petrolatum (pet.). With pet. as vehicle, it is impossible to repeatedly apply an exact volume/amount. This study was performed to investigate the inter- and intra-individual variation of pet. preparation applied at patch testing by 3 technicians. Weighing demonstrated that the 3 technicians had about the same precision in their pet. application. The investigation demonstrates that there is both an inter-individual (statistically significant) and intra-individual variation in the amounts of pet. applied at patch testing for the 3 technicians. Presently, there is no recommendation on what amount of pet. preparation to apply, which merits a decision to be taken based on thorough investigations on the appropriate volumes of pet. preparation to be applied in various patch test systems

Recommendation of appropriate amounts of petrolatum preparation to be applied at patch testing.

Background: No recommendation exists on the amount of petrolatum (pet.) preparation to be applied in a Finn Chamber (R) or van der Bend Chamber. Objectives: The aim of this study was to determine the appropriate amount of pet. preparation to apply in the Finn and van der Bend chambers. Methods: 12 volunteers were patch tested with green-coloured pet. in Finn and van der Bend chambers on the back on 3 occasions. Doses were 10, 15, 20, 25, and 30 mg initially and on second and third occasion, 10 mg was removed in van der Bend Chambers and 35 mg was added. On day 2, the test sites were scored. A negative test equalled a test area not covered to 100%. A positive test meant a completely green-coloured test area. Minor and major spreading was noted. The amount of pet. preparation yielding at most 5% negative reactions and having the least number of reactions with major spreading equalled the appropriate amount. Results: For van der Bend Chambers, all doses yielded more than 5% negative reactions. For the Finn Chamber (R), 30, 25, and 20 mg pet. yielded less than 5% negative reactions and with major spreading in 60%, 40%, and 25% of test sites. Conclusions: 20 mg pet. preparation was the optimal dose for the Finn Chambers (R)