Determination of cut-off positivity values in nasal challenge testing of patients with allergic rhinitis

Nasal challenge testing with allergens extracts is currently used to diagno se nasal allergy and, to a greater extent, in studies of pathophysiology of allergic rhinitis, The resulting nasal obstruction, measured as nasal airw ay resistance (NAR), is determined by rhinomanometry (RMM). The aim of this study ns to define a cut-off NAR value for a positive response in a nasal allergen challenge test. Forty-two grass-allergic adult patients and 40 non allergic adults were challenged out of the grass pollen season under standa rd conditions with timothy grass extract administered intransally in doses increasing from 10 to 1500 IU/mL. Inspiratory NAR was determined by compute rized anterior active RMM. The cut-off value for a positive test was determ ined from receiver operating characteristic curves plotted from these data with the LABROC1 computer program. In addition, the subjects' nasal cycle w as recorded during the four hours preceding the allergen challenge. The pat ients' mean NAR value at baseline (0.33 Pa/cc/sec) min,thm challenged with normal saline solution did not differ from those of the control subjects. T he patients, brit nor the control subjects, experienced typical nasal aller gic symptoms when challenged with the grass extract. The control subjects h ad no symptoms and their NAR did not change significantly when they were ch allenged with the same extract. All 42 allergic patients had measurable inc reases in NAR at the 800 IU/mL allergen dose, 19/42 patients had complete o bstruction (i.e., NAR unmeasurable) when challenged with the 1500 IU/mL dos e. The maximum diagnostic value (= sensitivity + specificity at the discrim inator position oil the receiver operating characteristic curves) was 1.96 with the 800 IU/mL dose. At that dose, the NAR cut-off value was 0.91 Pa/cc /sec, which was 2.7 times greater than their mean value at baseline. NAR va ried less than 1-fold between the maximum and minimum points of the normal nasal cycle ii? both groups of subjects. An increase of NAR of nearly three -fold during nasal allergen challenge compared to the baseline value determ ined by computerized anterior active RMM discriminates best patients with a llergic rhinitis from nonallergic adults.