We all know that food labeled gluten-free should be tested for gluten. Some of us are familiar with the tests that should be used to assess gluten content. But most of us don’t know how tricky it actually is to test for gluten. This blog is meant to start a conversation by pointing out the lack of standards when it comes to gluten assessment.


There are a lot of “shoulds” when it comes to testing food for gluten. Unfortunately just because something “should” be done does not mean that it will be done. A few of the “shoulds” are discussed below.

Food that is labeled gluten-free should be routinely tested at a third party laboratory well-versed in assessing food for gluten. The labs I have utilized are the Food Allergy Research and Resource Program (FARRP) and Bia Diagnostics (the lab used by Gluten Free Watchdog, LLC). Products should be tested using an ELISA that has been formally validated in a multi-lab performance evaluation at levels used for regulatory purposes. My pick is the R5 ELISA (Ridascreen Gliadin R7001 by R-biopharm) with cocktail extraction (Art. No. R7006, official R5-Mendez method). In addition, samples should be tested in duplicate—two extractions.

Beyond these three choices—lab, assay/extraction, and number of extractions—what happens to samples when they arrive at a lab is largely determined by the protocols established by the specific facility. Unfortunately, these protocols are not standardized between labs.

Note to manufacturers: It is your responsibility to specify to the lab the ELISA and extraction method you want used to test your samples. If you want your samples tested in duplicate you must request this as well.

At the lab

A product may arrive at a lab in several forms, including in retail packaging as sold to the consumer or as part of a retained sample from the manufacturer (not packaged for retail). Protocols for testing samples once they arrive at the lab are among the issues that need addressing.

All commercially available lab tests come with instructions from the manufacturer. The instructions for the R7001 assay from R-biopharm illustrate how much room there is for interpretation by individual labs. The instructions state to:

“Homogenize well a sufficient amount (at least 5 g or 5 ml) of sample (grind it thoroughly to powder and mix well or mix well the solution respectively).”

From the homogenized sample, 0.25 grams are added to the cocktail solution for testing.

Note: To homogenize a sample means to evenly distribute everything in that sample, including any gluten.


The instructions from R-biopharm for the R5 ELISA raise a lot of questions which need addressing as soon as possible:

Note: This is not an R-biopharm problem per se; these instructions are used merely to make a point.

  • Selecting the 5 gram sample

How does the lab make sure that the 5 gram sample selected for testing is representative of the entire sample sent to the lab?

Is the entire sample mixed before the 5 gram sample is taken?

Is the 5 gram sample taken from only one part of the entire sample?

Or are different aliquots (smaller samples) taken from the bottom, top, and middle of the package?

  • Homogenization

Once the 5 gram sample is selected, how does the lab go about homogenizing the sample?

Is it ground for a set period of time?

Is it ground to a certain particle size if it is a relatively dry sample?

What about samples that are moist or have a high fat content. How are they dealt with?

  • Reproducibility of results

How does the lab make sure the 0.25 gram sample actually tested is representative of the 5 gram sample?

Is the 5 gram sample tested in duplicate—are two 0.25 gram extractions tested

These are just a few of the many issues related to gluten testing that must be addressed. The Food and Drug Administration is not going to dictate to manufacturers how to go about ensuring their product is gluten-free or tell laboratories handling food samples how to go about testing product. These issues are left to the manufacturers and laboratories to determine. But due diligence is required from both laboratories and manufacturers to ensure that food labeled gluten-free is indeed gluten-free. Unfortunately, what constitutes “due diligence” has yet to be defined.

© 2012 by Tricia Thompson, MS, RD. All rights reserved. This article may not be reprinted, reposted, or republished without the express written permission of Tricia Thompson


Standards for testing food for gluten: Issues that need addressing