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

Nasal challenge testing with allergen extracts is currently used to diagnose nasal allergy and, to a greater extent, in studies of pathophysiology of allergic rhinitis. The resulting nasal obstruction, measured as nasal airway resistance (NAR), is determined by rhinomanometry (RMM). The aim of this study was 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 nonallergic adults were challenged out of the grass pollen season under standard conditions with timothy grass extract administered intranasally in doses increasing from 10 to 1500 IU/mL. Inspiratory NAR was determined by computerized anterior active RMM. The cut-off value for a positive test was determined from receiver operating characteristic curves plotted from these data with the LABROC1 computer program. In addition, the subjects' nasal cycle was recorded during the four hours preceding the allergen challenge. The patients' mean NAR value at baseline (0.33 Pa/cc/sec) and when challenged with normal saline solution did not differ from those of the control subjects. The patients, but not the control subjects, experienced typical nasal allergic symptoms when challenged with the grass extract. The control subjects had no symptoms and their NAR did not change significantly when they were challenged with the same extract. All 42 allergic patients had measurable increases in NAR at the 800 IU/mL allergen dose; 19/42 patients had complete obstruction (i.e., NAR unmeasurable) when challenged with the 1500 IU/mL dose. The maximum diagnostic value (= sensitivity + specificity at the discriminator position on 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 varied less than 1-fold between the maximum and minimum points of the normal nasal cycle in both groups of subjects. An increase of NAR of nearly three-fold during nasal allergen challenge compared to the baseline value determined by computerized anterior active RMM discriminates best patients with allergic rhinitis from nonallergic adults.