Exposure Sources, Amounts and Time Course of Gluten Ingestion and Excretion in Patients With Coeliac Disease on a Gluten-free Diet

Jocelyn A. Silvester; Isabel Comino; Lisa N. Rigaux; Veronica Segura; Kathy H. Green; Angel Cebolla; Dayna Weiten; Remedios Dominguez; Daniel A. Leffler; Francisco Leon; Charles N. Bernstein; Lesley A. Graff; Ciaran P. Kelly; Carolina Sousa; Donald R. Duerksen


Aliment Pharmacol Ther. 2020;52(9):1469-1479. 

In This Article


All recruited participants, which included 18 persons with coeliac disease on a GFD (12 female; median 41 years, range 21–77) and three healthy persons who consumed gluten regularly (1 female; ages 20, 36, 43 years) completed the study protocol (Table 1). As reported previously, participants with coeliac disease were generally asymptomatic although some reported mild symptoms; Coeliac Symptom Index (CSI) scores ranged from 19 to 40.[17] Coeliac diet adherence test (CDAT) scores were ≤14 suggesting adequate adherence; however, self-reported GFD adherence on the Gluten-Free Eating Assessment Tool short (GF-EATs) suggested higher rates of gluten exposure. Median serum TTG IgA at 24 months was 0.6 ULN (range 0.07–2.67), a more than 10-fold decrease from diagnosis, providing further evidence that gluten consumption had been reduced.

The mean number of pooled food samples was 17.4 (range 12–21). Those with fewer samples tended not to have a sample for the 04:01–10:00 time interval because they ate fruit and/or drank coffee/tea at breakfast. Three food samples were not collected (2 forgot; 1 participant travelled to the United States and was unable to return with the sample). Participants collected a mean 29.0 (range 22–30) urine samples and 4.2 (range 3–6) stool samples. Urine sample collections were missed due to urinary incontinence, working conditions and forgetfulness. There were no freezer failures.

Gluten in Food and GIP in Urine and Stool: Healthy Participants on a Gluten-containing Diet

The three participants on a gluten-containing diet collected samples during 62 of 63 possible time intervals. Nine (14%) food samples did not contain detectable gluten and one contained only 4 ppm gluten. Most (75%) contained very high amounts of gluten that exceeded the upper limit of the dynamic range of the assay (~600 ppm gluten, depending on sample dilution). Consistent with these findings, 67 of 88 (76%) urine samples contained between 2.2 and 58.5 ng GIP/mL, and all 12 (100%) stool samples contained detectable GIP.

Gluten in Food: Coeliac Disease Participants on a GFD

Coeliac disease participants following a GFD ate food prepared in their own home, at others' homes and at restaurants, and several participants travelled away from home. Overall, 25/313 (8%) pooled food samples tested positive. Based upon sample weights, median estimated gluten exposure was 2.1 mg per ingestion (range 0.2 to >80 mg). Foods that tested positive for gluten were consumed throughout the day and included baked goods, sausages, snacks and restaurant meals that were allegedly gluten-free (Table 2).

GIP in Urine and Stool: Coeliac Disease Participants on a GFD

Overall, 30/519 (6%) urine samples tested positive for gluten. Positive samples from eight participants contained 2.2–26.8 ng GIP/mL. For stool, 8/75 (11%) tested positive, containing 140–910 ng GIP per gram stool (Table 3). Five participants had at least one positive stool sample.

Association Between Suspected Gluten Exposure and Detection of GIP

For the coeliac disease participants, there were 20 days when gluten exposure was suspected, 14 of which were during the first seven days when food samples were collected. Twenty-seven foods were implicated related to concerns about cross-contact with gluten in restaurants or at home, specific ingredients (eg Worcestershire sauce), specific foods (eg cookie prepared by co-worker) and suspicions based upon symptoms. Most participants (73%) who suspected a gluten exposure had at least one positive food, stool or urine sample; however, only two participants correctly identified the culprit food (2 samples). There was only case in which gluten was detected when symptoms of gluten exposure were experienced. Four of the seven participants who did not suspect a gluten exposure had at least one sample that tested positive for GIP.

Correlation and Time Course of Documented Gluten Consumption and Detection of GIP in Urine or Stool

There were 25 documented gluten exposures from food, eight of which were associated with a positive urine sample within 36 hours and nine of which were associated with a positive stool sample 2–4 days later (Figure 2). The interval between consumption of a food sample that tested positive for gluten and GIP detection in urine ranged from 2–49 hours.

Figure 2.

Time course of gluten ingestion and excretion by participants with food, stool and/or urine sample(s) testing positive. Food samples are indicated by light blue squares, urine by yellow triangles and stool by brown circles. Samples in which gluten was detected are outlined in red. The left axis denotes the amount of gluten in milligrams detected in food samples and concentration of GIP in urine samples (ng/mL). Food samples testing over the upper limit of the assay are plotted outside the range and there is no symbol denoting the actual value. The right axis denotes the concentration of GIP in stool (ng/g). Results from the 3 healthy controls who consumed gluten regularly (panel A) and the 12 participants following a GFD who had any sample with detectable GIP (panel B) are shown. All samples from the other 6 participants on a GFD tested negative. Participant 11 consumed 4.7 mg gluten (17 ppm) in rice grits and potato chips and 0.2 mg gluten (4 ppm) in nacho chips and caramel candies 3 d later. In both cases, urine tested positive for GIP 49 hr after exposure. Participant 12 consumed 12.1 mg gluten (35 ppm) on day #2, 10.1 mg gluten (21 ppm) on day #3, 1.3 mg gluten (11 ppm) on day #4 and 9.7 mg gluten (42 ppm) on day #5. Urine was positive for GIP within 4 hr of the first two exposures, and 25 hr after the fourth exposure. Stool produced on the night of day #4 contained GIP. Participant 17 consumed 0.8 mg gluten (6 ppm) on day #1, 1.4 mg gluten (5 ppm) on day #3 and 1.8 mg gluten (45 ppm) on day#5. GIP were detected in urine 7.5 hr after the first exposure and 2 hr after the third exposure. Stool collected on the morning of day #8 contained detectable GIP. Participant 14 had consumed >20 mg gluten (>100 ppm) on day #2 with GIP detected in stool collected 48 hr later. Urine samples tested negative; however, no samples were obtained between 6 and 24 hr after gluten exposure. Participants 2, 5, 7 and 8 each had at least one exposure to up to 2.1 mg gluten with no GIP detected in any contemporaneous urine or stool samples. Participant 16 had repeated gluten exposure with 10 (59%) of food samples collected containing detectable levels of GIP (no samples tested positive on day #6). Stool samples collected on days 4, 5, 8 and 9 all contained GIP. GIP were not detected in any urine sample collected day #1 through day #4, but at least one urine sample contained GIP on day #5 through day #10