Patch testing is the only practical, scientific,
and objective method for the diagnosis of ACD. It is indicated in
patients with a chronic, pruritic, eczematous, or lichenified dermatitis in whom ACD is suspected. Patch test reactions are affected by
oral corticosteroids (>20 mg of prednisone per day or its equivalent), cancer chemotherapy, or immunosuppressive drugs but not
by antihistamines. Topical corticosteroids on the patch test site
should be discontinued for 5 to 7 days before patch testing.