How to Manage a Positive Allergen Residue Result when Testing Your Food Product

Editor’s note: This is part 1 of a two-part series on allergen residue results. Part 1 focuses on how to confirm a positive result and Part 2, which published in our February/March 2021 issue, focuses on steps to take once a result has been affirmed.

Positive results in allergen testing of food products can sometimes be quite unexpected and disconcerting. This is particularly true when testing finished food products ready for distribution and sales, or ingredients procured for a manufacturing run in the near future. Positive allergen residue results are not so surprising when testing to assess the effectiveness of cleaning protocols on shared equipment, especially when qualifying a new cleaning procedure, but a positive result is disturbing if the cleaning protocol has been assessed on numerous previous occasions with no positive results.

Oftentimes, ingredient or finished product samples are sent to external commercial laboratories to confirm that detectable allergen residues are not present. Swabs and final clean-in-place rinse waters are also sent to commercial laboratories, typically as a third-party check to demonstrate consistency with in-plant analysis using qualitative methods such as lateral flow devices (LFDs). In some cases, the product, ingredient, and/or process have been checked on multiple occasions with no previous positive detection of allergen residues. Even in cases where allergen testing has not been performed previously or testing was sporadic, the positive result is still an unpleasant surprise. The situation becomes even more alarming if the testing was performed by a valued customer, an auditor, or a regulatory inspector.

What should you do when you get that unexpected positive result? First of all, take three deep, calming breaths, and step back from the ledge. Then, get into investigative mode. Sometimes, the recipients of an unexpected positive result will immediately wonder if the external laboratory made a testing error and/or claim that the result is a false positive. That possibility needs to be assessed but is not the only possible explanation. Other possibilities include a manufacturing error (cross contact), a contaminated ingredient, a packaging error, or a failure of the allergen cleaning protocol.

We know from experience that recipients of unexpected positive results from an external lab report may immediately reach out to their external laboratory or reach out to the Food Allergy Research and Resource Program (FARRP) for assistance. While we are okay with sharing your pain at this stage, know that our initial goal will be to put you into investigative mode to get enough information so that we might really be able to help you with a thorough root cause analysis and/or risk assessment.

Carefully Examine That Laboratory Report

The laboratory report should, but will not always, contain critical information. First, double check the sample identification information on the report to ensure the laboratory report contains the test result for the sample(s) that you sent for analysis. The laboratory report will contain the analytical result(s), but most importantly, it should also contain the units, usually ppm for allergen analysis. However, these laboratory reports may not always list the calibrant. For example, when testing for milk residues, 10 ppm β-lactoglobulin (BLG) is not the same as 10 ppm non-fat dry milk (NFDM). In fact, 10 ppm BLG is equivalent to 286 ppm NFDM because BLG is roughly 10% of total milk protein and NFDM contains about 35% protein. The laboratory report should, but will not always, contain the identity of the method used to acquire the result. Many external laboratories use commercial enzyme-linked immunosorbent assays (ELISAs) for detection of allergen residues. Citing milk allergen analysis again as our example, at least six different ELISA kit companies (even more on an international basis) produce milk ELISA kits, and several of them make multiple milk ELISA kits with different targets (total milk, casein, or BLG) and different calibrators (non-fat dry milk, soluble milk protein, casein, or BLG). The choice of the milk ELISA kit can make a difference for your results and will certainly affect the interpretation of the seriousness of the finding to the potential risk of the product.