Development and evaluation of a rapid assay for the diagnosis of immunoglobulin E-mediated type I allergies.

A characteristic feature of type I allergies is the presence of allergen-specifi c immunoglobulin E (sIgE) [1,2]. Thus, the detection of sIgE, in addition to obtaining a clinical history and performing a skin prick test (SPT), is important for allergy workup. Historically, sIgE to various allergens was analyzed by radioallergosorbent test using allergen-coupled cellulose paper discs. Later on, the enzyme allergosorbent test and the reversed allergosorbent test were used for the detection of sIgE [3]. In recent years, rapid assays for the detection of sIgE as point-of-care diagnostics have been developed using various strategies [4]. The objective of this study was the technical evaluation of 2 rapid assays (ALFA Seasonal Screen [ALFA S] and ALFA Perennial Screen [ALFA P]) for the detection of sIgE to the most common inhalant allergens. Serum samples (n = 50) were tested by ALFA and sIgE was analyzed for all single allergens utilized in ALFA allergen screens by ALLERG-O-LIQ (Dr. Fooke Laboratorien GmbH, Neuss, Germany), a reverse-type, quantitative immunoassay (WHO 75/502 calibrated). The maximum kU A /L value (ALLERG-O-LIQ) of each sample was used as a reference value. For comparison of ALLERG-O-LIQ and ALFA, samples were defi ned as ALLERG-O-LIQ positive when the sIgE result was ≥ 0.35 kUA/L. Appropriate statistics were used. sIgE profi les of specimens were generated by ALLERG-OLIQ. Twenty-six (52.0%) samples were positive for sIgE to at least 1 perennial and 45 (90.0%) to at least 1 seasonal allergen. Twenty-four (92.3%) of the 26 perennial-positive samples were also positive by ALFA P and 38 (84.4%) of the 45seasonal-positive samples were also positive by ALFA S. When a cutoff value of 1.6 kUA/L was used, the sensitivity increased to 100% for both ALFA tests. None of the ALLERG-O-LIQ-negative samples tested positive using the respective ALFA assay (100% specifi city). The kappa statistic was 0.92 (P<.0001) for ALFA P and 0.52 (P=.0003) for ALFA S compared to the ALLERG-O-LIQ. A serologic characterization of the sample cohort is shown in the Figure. In recent years, sIgE profi le and screening tests have been developed using different protocols. In 2004, comparison of ALLERG-O-LIQ and the ImmunoCAP system showed good A lle rg en S pe ci fi c I gE , k U A /L