Sten Dreborg, Antonio Basomba, Thorvald Löfkvist, Margareta Holgersson and Christian Möller
Background: Parallel line bioassay (PLBA) has been acknowledged to be the gold standard for estimation of changes in reactivity, e.g., in RAST and ELISA inhibition tests.
Objective: To study correlations between two simple methods for evaluation of changes in skin prick test (δSPT), using the slope of the allergen dose response (drra) in relation to PLBA.
Methods: Skin prick test data from two published immunotherapy trials were used. In a D. farinae trial we used duplicate tests with three fixed ten-fold concentrations and in a P. judaica trial three tenfold individually chosen allergen concentrations causing wheals of similar size to that of histamine dihydrochloride 10 mg/mL, tenfold lower and tenfold higher concentration. Evaluation of the δSPT by PLBA, and two simple methods were correlated. In the D. farinae trial δSPT was compared to the change of conjunctival threshold concentration.
Results: The δSPT as measured by both the simple methods gave similar results to that of PLBA (p<0.001). The δSPT was around 30-fold, i.e., about 3% of the pre-treatment reactivity. The δSPT correlated with the δCPT threshold concentration.
Conclusions: Estimation of the δSPT during therapy expressed as change in concentration using simple methods based on the slope of the drra correlated well to changes by PLBA and CPT and should therefore be used both in clinical research and in practice.