There is no single PT series or kit that will identify all of the allergens in a patient's environment.
It is generally thought that 20 to 30 allergens in routine screening tests can identify 50% to 70% of clinically relevant ACD.
However, a study by the north American contact dermatitis group (NACDG) showed that the use of 20 screening allergens commercially available in the united states from july 1994 to june 1996 accounted for only 54.1% of the patients with a positive reaction.
the additional 30 allergens on the NACDG screening series accounted for an additional 47% of patients with positive results.
Among these patients,12.4% might have been misdiagnosed as nonallergic,and an additional 34.4% would not have their allergies fully defined if a smaller PT series were used.
therefore, the usefulness of patch testing is enhanced with the number of allergens tested, and allergens not found on commercially available screening series in the united states frequently give relevant reactions.