Diagnosis of fungal allergy: Comparison of detection of allergens from germinating fungi (Halogen method) with Pharmacia UniCap assay and skin prick tests

Abstract

Rationale Accurate diagnosis of allergy to specific fungal species is confounded by the variability in allergens occurring with different diagnostic systems. We compared the Halogen immunoassay (HIA), where allergens from germinating fungal spores are directly bound to protein binding membranes (PBM), with the Pharmacia UniCap assay (CAP) and with skin prick tests (SPT). Methods Serum from 60 subjects was used; 30 were SPT positive to at least one of Alternaria alternata or Aspergillus fumigatus and another 30 subjects were SPT negative to fungi. All were analyzed by CAP against A. alternata, A. fumigatus, Cladosporium herbarum and Epicoccum nigrum. For HIA, spores from reference cultures belonging to these species were germinated on PBM, laminated and then probed with each serum. The intensity and occurrence of the resultant IgE immunostaining haloes around spores were quantified by two independent examiners using an ordinal ranking system. Results In HIA, the between-examiner ordinal ranking scores only differed for C. herbarum (Wilcoxon non-parametric analysis), p=0.03. Two SPT negative sera were identified by HIA and CAP to be positive to A. alternata. For the SPT positive sera, significant non-parametric correlations (p<0.0001) were found between HIA and CAP scores as follows: A. alternata (r s=0.75), A. fumigatus (r s=0.56), E. nigrum (r s=0.63) and C. herbarum (r s=0.51). Correlations between HIA and SPT were significant for A. alternata (r s=0.62, p<0.0001) but not for A. fumigatus (r s=0.17, p<0.1790). Conclusions Overall, HIA is a new immunodiagnostic technique that correlates significantly with CAP and to a lesser extent with SPT, which may be due to extract variability and system differences.