What is the role of immunologic testing in the workup of allergic fungal sinusitis (AFS)?

Updated: Mar 16, 2018
  • Author: John E McClay, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Answer

Immunologic testing for allergens

  • RAST versus skin testing

    • Patients with allergic fungal sinusitis (AFS) generally demonstrate positive skin tests and in vitro (RAST) responses to fungal and nonfungal antigens. Manning et al, who compared 16 patients with histologically confirmed allergic fungal sinusitis (AFS) with a control group of patients with chronic rhinosinusitis, first demonstrated the sensitivity of RAST. Levels of fungal-specific IgE were uniformly elevated in all patients with allergic fungal sinusitis (AFS) and corresponded to the results of fungal cultures. In contrast, levels of fungal-specific IgE were not elevated within the control group. Moreover, patients with allergic fungal sinusitis (AFS) appear to demonstrate a broad sensitivity to a number of fungal and nonfungal antigens. Mabry et al have reported their experience, which indicates that patients with allergic fungal sinusitis (AFS) are allergic to multiple fungal antigens and to many typical nonfungal antigens.

    • Preliminary information suggests that methods of quantitative skin testing (in vivo) may provide even greater sensitivity ratings than RAST in patients with allergic fungal sinusitis (AFS). RAST traditionally has been considered less sensitive than skin testing during the investigation of atopy involving fungi. This has been attributed to technical problems, such as difficulty in binding the mold antigen to the carrier substrate.

    • To study the validity of this concept, Mabry et al prospectively evaluated 10 patients with allergic fungal sinusitis (AFS) for sensitivity to 11 pertinent fungi by both RAST and dilutional intradermal testing. A predictable correlation between RAST and skin test scores was observed in many, but not all, patients. Most often, this disparity was in the form of greater sensitivity indicated by skin testing than by RAST, sometimes differing by as many as 3 classes.

    • The lack of concordance was not confined to testing for fungi cultured from the sinuses, nor was it more or less pronounced in the case of dematiaceous fungi. The most likely causes for the disparity were thought to involve subtle differences in antigens used in skin test material as compared to RAST standards. Additionally, skin testing allowed observation of delayed and late-phase reactions, a measure not possible by specific IgE testing with RAST. This study appears to emphasize the importance of both skin testing and specific IgE testing via RAST in initial evaluation of patients in whom allergic fungal sinusitis (AFS) is suspected.


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