Comparison of different diagnostic products for skin prick testing.

BACKGROUND Different in vivo methods are used to quantify the amount of allergens in products for skin prick testing. It is unclear how this impacts on the correct diagnosis of allergies. AIM OF THE STUDY We compared the allergenic potency of three commercial extracts for skin prick testing and evaluated batch-to-batch differences within each product. METHODS Patients with a mono-sensitization (specific IgE level > 0,70 KU/L, ImmunoCAP, Phadia) to Phleum pratense (N=21), Parietaria judaica (N=20) or Dermatophagoides pteronyssinus (N=28) were evaluated by standard skin prick testing and with the end-point dilution technique using commercial products from Stallergenes (A) (Antony, France), Lofarma Allergeni (B) (Milan, Italy) and ALK Abellò (C) (Hoersholm, Denmark). Results were expressed as mean areas of the wheal (cut-off for positive reactions: 7 mm2). RESULTS With standard prick testing, the following differences in wheal areas were found: Phleum, C higher than B (p=0.0454); Parietaria, C higher than A (p=0.094); Dermatophagoides, C higher than A (p=0.021). With limiting dilution testing, the following differences in dilutions yielding positive skin prick tests were found: Phleum, C and B higher than A (p=0.0391 and 0.0039, respectively); Dermatophagoides, C higher than A and B (p=0.0010 and 0.0156, respectively). In the batch-to-batch comparison, mean differences between wheal areas of compared undiluted solutions did not significantly differ in any allergen tested, although in single cases large differences were observed. At the 1 to 64 dilution, agreement was significant only with Dermatophagoides from Manufacturer C (p= 0.262). At the 1 to 16 dilution, agreement was significant with Phleum from Manufacturer C (p=0.0116) and with Dermatophagoides from Manufacturer B and C (p=0.0239 and 0.0001, respectively). At the 1 to 4 dilution agreement was significant with Dermatophagoides from the three considered Manufacturers (p=0.0189, 0.0052 and 0.0077, respectively) and with Phleum from Manufacturer B and C (p=0.0336 and 0.0113, respectively). CONCLUSION There are significant differences among commercially available diagnostic products for skin prick testing.