Lateral Flow Tests for Allergy Diagnosis: Point-of-Care or Point of Contention?

Abstract

developed for detection of allergen-specific IgE and could have utility for allergy diagnosis. However, it is only recently that an allergy diagnostic LFT has been introduced to practice. In this issue, Sanchez-Bahillo et al. [6] compare the performance of an allergy diagnostic LFT (ImmunoCAP Rapid, Phadia, Sweden) with skin prick testing in a cohort of allergic children from Cartagena (Spain) who were recruited as part of the ISAAC Phase II study. The IgE LFT is a plastic device with a well where serum, plasma or whole blood can be applied. The serum diffuses along 2 parallel strips where different allergen extracts have been applied and specific IgE is detected using goldlabeled anti-IgE incorporated in the test strip. The IgE LFT measures IgE to cat, dog, birch, olive, mugwort, wall pellitory, dust mite, timothy, egg white and cow milk on lines that appear as 2 parallel ‘barcodes’ contained within the plastic housing. Plasma samples from 270 children (aged 9–12) who had been skin tested using the ISAAC phase II protocol were compared in the IgE LFT using a 4-point scoring system (from value 1 indicating a lightly visible line to value 4 indicating a line with greater intensity than that of the positive control). By skin prick test, only 4–7% of patients were sensitized to birch, timothy grass or pellitory, which was insufficient for comparison with IgE LFT. The data was analyzed based on results from patients with positive skin tests to D. pteronyssinus (n = 123), olive (n = 62) and cat (n = 48) using Cohen’s statistic and the Z statistic. Considering an IgE LFT score of 1 to be positive, there was 90% Lateral flow technology, or ‘point-of-care’ (POC) testing, has been a staple of the in vitro diagnostics and medical device industry since the 1980s. Originally, developed for use in pregnancy tests, the technology is widely used not only in pregnancy tests, but in tests for drugs of abuse, tuberculosis, HIV, cardiac markers, infectious diseases and food testing, in what is now a multi-billion Euro market. Lateral flow tests (LFT) enable small chemicals, hormones, drugs, antigens, haptens and antibodies to be measured rapidly, with high sensitivity and specificity. Typically, they involve antibody coupled to nitrocellulose membrane as a line on an immuno-chromatographic strip. Analytes diffuse from a well along the strip and release a detector antibody (labeled with colloidal gold or latex particles). The soluble analyte/antibody complexes diffuse to the capture antibody line where they are deposited (if analyte is present) and form a red (gold) or blue (latex) line which indicates a positive test. Modifications of this format – including use of magnetic beads, nanoparticle-based signal amplification techniques, DNA barcodes and digital-style readouts for multiplexed analyte detection – are being developed for use in a wide range of POC tests [1] . The POC tests are designed for use in doctors’ offices, hospital clinics, healthcare centers, pharmacies and consumers and provide a quick, accurate and inexpensive diagnostic test. In the 1990s, lateral flow technology was first applied in the allergy field for the detection of dust mite and other allergens in environmental samples [2–5] . It was clear at the time that with various modifications, LFT could be Published online: February 26, 2010