Clinical reliability of diagnostic tests in allergic rhinoconjunctivitis

To determine the diagnostic value and precision of the quantitative skin test (QST), RAST, specific nasal (NPT) and conjunctival (CPT) provocation tests, we studied 91 patients, suffering from allergic rhinoconjunctivitis with positive skin prick tests (SPT) to common allergens, among whom sixty-nine of them had symptoms related to the positive SPT, and 22 had no clinical correspondence. In these two groups, by comparing the threshold of positivity, we investigated whether there was any parallelism between responses to the tests considered. We also compared the level of specific IgE (RAST) to the wheal-areas evoked by preliminary SPT for the corresponding allergen in order to detect any quantitative relationship between these investigations. Increasing concentrations of standardized allergen extracts (from 10 to 100,000 BU/ml) were used in all in vivo tests. NPT was evaluated on the basis of multiple recordings of nasal resistances by anterior passive rhinomanometry. QST proved to correlate well with RAST and its easier method ensures it a major role in assessing the levels of allergic sensitization. SPT wheal-areas and RAST vales correlated well only for grass and birch, presumably because of better standardization of these allergen extracts. When provocation tests, especially NPT, were positive, patients were almost always symptomatic for the allergen tested (high positive predictive value). Likewise, 21 out of the 22 asymptomatic subjects had negative NPT (high specificity). These results suggested the utility of standardized provocation tests in order to restrict diagnosis to the truly causative allergens in patients with multiple positive SPT results.