Assessing the LEO Gluten Tester did not go as expected: Testing wheat bread for gluten

Long story short: Wheat bread was tested for gluten using the LEO tester. After 3 minutes, there was a faint line above the E as confirmed by the LEO app. According to the LEO website, “If you see a line above the “E” of LEO then the sample is 10 PPM or less.” Hmm.

Long story long: Over a two day period (that included a lot of thinking and a phone chat with Adrian Rogers, a specialist in immunoassay development with a focus on gluten and food allergen detection), wheat bread was tested for gluten using the LEO.

For the first two tests, the testing procedure was followed as specified in the instructions. The swab was moistened and then rubbed across the bread five times. The swab was placed into the solution tube, swirled around 5 times, and removed after 30 seconds. The vial was capped, given a good shake, and then 3 drops were added to the sample well on the LFD device. After 3 minutes, the result was read.

Both tests showed a weak line above the E after 3 minutes (the second test reading was confirmed by the LEO app). According to the LEO website, “If the line is very faint about the “E”, then the test is very close to being over 10 PPM…”

For the third test, crumbs of bread were added directly to the test solution. This test also showed a weak line above the E after 3 minutes.

For the fourth test, only the solution in the vial was tested (in other words, no food was added via a swab or directly). The result was a stronger line above the E.

For the fifth test, water was mixed with bread and this heavily moistened bread was tested by swirling the swab in the mixture. There was no line above the E after 3 minutes. According to information provided with the test kit, “If you do not see a line above the “E” do not eat it.”

What might be going on? With some help from Adrian, that’s what we are trying to figure out. Putting aside the issue of collecting dry food on a swab, a clue may be provided from the testing done on the solution in the vial (no food added).

After 3 minutes, the LFD looked like this…

But after 8 minutes, the LFD looked like this…

It appears that the LFD continued to develop for a period of time after 3 minutes. How might this have impacted the bread testing? The faint E line when testing the slices of bread and the crumbs started to disappear fairly quickly after the 3-minute mark. Maybe this is intentional? It is hard to say without seeing a validation report.

If you would like to watch a video explanation of the testing process, please see

https://drive.google.com/file/d/1_3DbA4z0OIeUCyJbgWaHqFGKNg-caljR/view?usp=sharing

Gluten Free Watchdog reached out to the LEO team and walked them through our testing. They were invited to provide a statement for posting. From Seaton Smith, “The Leo Team and I were surprised by the test results compared to other testing data. We take the GFWD test results very seriously and believe that the results were due to the sample size and type of food. We feel that the tester performed as designed but based on this report we have added to our current testing procedures that will be emailed out to all of our customers and posted on our website under the FAQ section.”