Determination of provocation threshold of the nasal provocation test (NPT) in patients with allergic rhinitis

On performing the nasal provocation test (NPT), the question arises, whether to use different concentrations of the allergen extract, and whether there must be a difference in the way of performing the test on testing different allergens and allergen groups. It is also not clear, which concentration should be used in order to postulate a positive reaction in case of the presence of an actual sensibilisation without triggering the over-stimulation reactions, such as those of the lower aspiratory airways. In this study, 101 patients with allergic rhinitis have been tested by means of the NPT. The patients demonstrated a positive finding regarding the clinical history, skin-test and RAST towards one or more of the following allergens: house dust mites, molds, cat hair, grass and birch pollen. A positive NPT was registered in 93 cases using three different allergen concentrations: 1 : 100 (1000 SQ-U/ml), 1 : 10(10,000 SQ-U/ml) and 1 : 1 (100,000 SQ-U/ml) of the corresponding allergen extract. Eight patients showed no positive reaction. Our study demonstrates the need to employ undiluted concentrations of the allergen extracts in order to trigger an adequate reaction on testing with the so-called weak allergens such as the house dust mites and molds as a routine diagnostic measure. On the other hand, when testing with the so-called potent allergens such as cat hair extract, grass or birch pollen extract, a higher dilution of the allergen extract, for example 1 : 100 diluted allergen concentration is to be carefully started with, since a positive reaction can already be triggered with this concentration in a relatively high percentage of the cases. The results of our study can be considered as a further important recommendation to the standardization of this important diagnostic measure.