When is a positive nasal challenge test clinically relevant?

339 subjects with a clinically manifest or latent allergy to different allergens were tested intranasally: 163 with grass pollens, 19 with tree pollens, 46 with cat fur, 23 with dog hair, 79 with mites and 9 with horse hair. Two thirds of the patients with a latent allergy towards pollens either reacted to a pollen concentration of 1% w/v or not at all, one third responded to 0.1% w/v. Two thirds of the pollinosis patients reacted at 0.01% w/v, one third at 0.1% w/v. Threshold dosages were also found for animal fur: The limits are at 1.5% w/v (manifest allergy) and 150% w/v (latent allergy) and the transitional range at 15% w/v. No threshold was found for mites. The study shows that for certain allergens there exist threshold concentrations which should not be exceeded. Where there is no threshold dose, as e.g. with mites, the nasal test is no more informative than the skin test.