ELISA kits… quantitative or not?
Service laboratories and industries, as well as governmental bodies, rely on ELISA kits for the detection of food allergens. Recently, a number of guidelines for the validation of ELISA methods for detecting allergens have been issued by the analytical chemistry community (AOAC) and by technical bodies that promote standardization (ISO, CEN). Today, however, there are neither fully validated confirmatory methods nor complete Certified Reference Materials (though some Reference Materials are available; see R. Poms). Without any internationally accepted thresholds, there is an expectation that tests kits are designed to detect the lowest possible concentrations of the target molecules. The scientific literature, however, as well as the results of proficiency tests, reveal doubts about recovery and detectability in processed food. To gain further insight, we interviewed three large test kit producers (R-Biopharm, Romerlabs, Neogen) and two smaller companies that also manufacture test kits, one producing LFDs (Zeulab) and the other producing RT-PCR kits (Generon). Kit Sensitivity The Limit of Detection (LOD) of assays is an important element for kit purchasers. In Australia and New Zealand, following the VITAL approach, the target concentration depends on the potency of an allergen to exert an allergic reaction, but also on the amount of allergen in the food portion. However, most of the rest of the world does not agree with this threshold approach and industries generally look for the method with the lowest LOD. For some customers, requests for the lowest possible LOD are related to the absence of actual accepted limits, as a representative of R-Biopharm explains. “If the VITAL limits were accepted nobody would ask for lower LODs. This is what happened in case of gluten, for instance. Very few customers ask for a gluten sensitivity lower than 20ppm.” A representative of Neogen states, “Some industries are establishing the cut-offs for each product after considering proposed thresholds and portion sizes while others simply look for the kit with the lowest LOD. At present, it is not clear if the threshold approach will be accepted throughout the industry.” “To look for the lowest LOD has one risk,” said R-Biopharm’s representative. “In some cases, it could be very critical to manage this information into the real production site. If industries start finding very low but detectable concentrations then, considering there is no threshold, what should they do? So there should be a balance: testing must guarantee enough protection for the consumer but at the same time testing should not create unnecessary burdens for the food industry.” According to a representative of Generon, clients usually request the most sensitive kit, but there is little knowledge about the concept of LOD in matrices, thus creating concern about the need for matrix validations for ELISA kits. Because these kits are often considered “universal,” the necessity of adding further matrix validations can disappoint clients.
How have kit LODs been established? Considering the absence of legal thresholds and the lack of suitable Certified Reference Materials (CRM) for many allergens, calculating the LOD of any kit is a challenge. “Our kits are validated following the most up-to-date validation guidelines,” declares a representative of Zeu. “In the case of
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