Gluten immunogenic peptide excretion detects dietary transgressions in treated celiac disease patients

Table 1 Characteristics of tests for detecting gluten immunogenic peptides in stool and urine

Method	Type of sample	Limit of detection	Time tobe excreted1	Time of GIPclearance1	Detectable levels ofgluten intake
ELISA
LFIA; PoCT	Stool	60-150 μg/g	2 d	2-7 d	>40 mg/d
LFIA; PoCT	Urine	2-3 ng/mL	1-12 h	24-48 h	40-500 mg/d2

¹Time after gluten intake;

²The ingestion of 50mg of gluten per day can be detected in urine with a sensitivity of 15%, and the ingestion of 500mg gluten per day can be detected with a sensitivity of 90% when analyzing the first urine in the morning[24]. GIP: Gluten immunogenic peptides; ELISA: Enzyme-linked immunosorbent assay; LFIA: Lateral-flow immunochromatographic assay; PoCT: Point-of-care test.

Table 2 Demography, clinical and biochemical characteristics and results of the 3-d dietary reports of the complete population according to clinical characterization at enrollment

Parameter	Asymptomatic	Symptomatic
Number of individuals (females)	25 (21)	19 (19)
Age at enrollment, median (range)	50 (29-82)	51 (25-59)
Years on a GFD, median (range)	8 (2-48)	9 (4-27)
Body mass index, median (range)	25 (19-32)	25 (19-38)
GSRS, median score (range)	1.16 (0.2-2)	2.44 (2-3.6)a
Serology
Serum IgA tTG
Median concentration (range)	11 (2-100)	8 (3-200)
Number of patients with normal tests (%)	19/24 (79.2)	14/18 (77.8)
Serum IgA DGP
Median concentration (range)	19 (2-78)	12 (200-5)
Number of patients with normal tests (%)	12/22 (54.5)	10/18 (55.6)
Excretion of GIP (stool and urine)
N of positive samples (%)	10/47 (21.3)	3/36 (8.3)
3-d dietary recall (completed)	(47)	(36)
Strict adherence
Number of patients (%)	26 (55.3)	27 (75.0)
No adherents
Number of patients (%)	21 (44.7)	9 (25.0)

^aP <0.0001.GFD: Gluten-free diet; GIP: Gluten immunogenic peptides; GSRS: Gastrointestinal Symptom Rating Scale; DGP: Deamidated gliadin peptide.

Table 3 Serology, dietary adherence (3-d recall) and gluten immunogenic peptide excretion tests in samples from patients with celiac disease responding to the gluten-free diet (asymptomatic cases)

Patient No.	Serology		First set of determinations				Second set of determinations
	IgAtTG AU/mL	IgADGPAU/mL	Dietary report	GIP in stool ELISA μg/g	GIP in stool PoCT	GIP in urine PoCT	Dietary report	GIP in stool ELISA μg/g	GIP in stool PoCT	GIP in urine PoCT
1	12	10	Strict	< 0.16	-ve	-ve	Strict	< 0.16	-ve	-ve
2	11	36	NA	0.19	ND	-ve	NA	< 0.16	ND	-ve
3	14	13	Strict	< 0.16	-ve	-ve	Strict	< 0.16	-ve	-ve
4	5	7	Strict	< 0.16	-ve	-ve	Strict	< 0.16	-ve	-ve
5	17	22	Strict	< 0.16	-ve	-ve	Strict	< 0.16	+ve	-ve
6	32	58	NA	< 0.16	-ve	-ve	NA	ND	ND	ND
7	16	41	Strict	< 0.16	-ve	-ve	Strict	< 0.16	-ve	-ve
8	6	11	NA	< 0.16	-ve	+ve	NA	< 0.16	-ve	-ve
9	33	18	NA	< 0.16	-ve	-ve	NA	< 0.16	-ve	-ve
10	2	2	NA	0.38	+ve	-ve	NA	0.75	+ve	-ve
11	40	23	Strict	< 0.16	-ve	-ve	Strict	< 0.16	-ve	-ve
12	12	6	NA	< 0.16	-ve	-ve	NA	< 0.16	-ve	-ve
13	8	20	Strict	< 0.16	-ve	-ve	Strict	< 0.16	-ve	-ve
14	8	25	Strict	< 0.16	-ve	-ve	Strict	< 0.16	-ve	-ve
15	9	ND	NA	< 0.16	-ve	-ve	NA	< 0.16	-ve	-ve
16	10	25	NA	< 0.16	-ve	-ve	NA	0.66	+ve	+ve
17	15	ND	Strict	0.26	-ve	-ve	Strict	< 0.16	-ve	-ve
18	32	16	Strict	< 0.16	-ve	-ve	Strict	< 0.16	-ve	-ve
19	ND	ND	NA	< 0.16	-ve	-ve	NA	< 0.16	-ve	-ve
20	11	21	Traces	< 0.16	-ve	-ve	NA	ND	ND	ND
21	6	13	Traces	< 0.16	-ve	-ve	NA	< 0.16	-ve	-ve
22	100	78	ND	0.66	-ve	+ve	ND	ND	ND	ND
23	8	8	Strict	0.26	-ve	-ve	Strict	0.75	-ve	-ve
24	17	22	Strict	< 0.16	-ve	-ve	Strict	< 0.16	-ve	-ve
25	6	6	Strict	< 0.16	-ve	-ve	Strict	< 0.16	-ve	-ve

Dietary assessments were categorized as “strict” (patients with no transgression detected) or no adherence (by sources: transgression by foods with potential gluten sources or by traces: patients with potential intake of gluten traces). Gluten immunogenic peptidesin stool by enzyme-linked immunosorbent assay<0.156: no gluten excretion detected. NA: No adherence;ND: Not determined and excluded from analysis; -ve: Negative result; +ve: Positive result; DGP: Deamidated gliadin peptide; GIP: Gluten immunogenic peptides; ELISA: Enzyme-linked immunosorbent assay; PoCT: Point-of-care test.

Table 4 Celiac serology, dietary adherence assessed by dietary report and gluten immunogenic peptide excretion tests in samples from patients with celiac disease not responding to the gluten-free diet (symptomatic cases)

Patient No.	Serology		First set of determinations				Second set of determinations
	IgAtTG AU/mL	IgADGPAU/mL	Dietary report	GIP in stool ELISA μg/g	GIP in stool PoCT	GIP in urine PoCT	Dietary report	GIP in stool ELISA μg/g	GIP in stool PoCT	GIP in urine PoCT
1	3	5	Strict	< 0.16	ND	ND	NA	< 0.16	-ve	ND
2	15	9	NA	< 0.16	ND	ND	Strict	< 0.16	ND	ND
3	30	75	Strict	0.38	ND	ND	Strict	< 0.16	ND	-ve
4	77	> 200	NA	< 0.16	-ve	-ve	NA	< 0.16	-ve	-ve
5	8	1	Strict	< 0.16	-ve	-ve	Strict	< 0.16	-ve	-ve
6	4	6	Strict	< 0.16	-ve	-ve	NA	< 0.16	-ve	-ve
7	3	13	Strict	< 0.16	-ve	-ve	Strict	< 0.16	-ve	-ve
8	27	11	Strict	ND	ND	-ve	Strict	< 0.16	-ve	-ve
9	3	39	Strict	< 0.16	ND	-ve	Strict	< 0.16	-ve	-ve
10	5	4	Strict	< 0.16	-ve	-ve	Strict	< 0.16	-ve	-ve
11	> 200	67	Strict	< 0.16	-ve	-ve	Strict	0.42	-ve	-ve
12	8	10	Strict	< 0.16	-ve	-ve	Strict	< 0.16	-ve	-ve
13	3	35	NA	< 0.16	-ve	-ve	Strict	< 0.16	+ve	-ve
14	ND	ND	NA	< 0.16	-ve	-ve	NA	< 0.16	-ve	-ve
15	12	12	Strict	< 0.16	-ve	-ve	Strict	< 0.16	-ve	-ve
16	14	25	Strict	< 0.16	-ve	-ve	ND	ND	ND	ND
17	8	9	Strict	< 0.16	-ve	-ve	ND	ND	ND	ND
18	17	36	Strict	< 0.16	-ve	-ve	Strict	< 0.16	-ve	-ve
19	8	24	NA	< 0.16	-ve	-ve	Strict	< 0.16	-ve	-ve

Dietary assessments were categorized as “strict” (patients with no transgression detected) or no adherence (by sources: transgression by foods with potential gluten sources or by traces: patients with potential intake of gluten traces). Gluten immunogenic peptides in stool by enzyme-linked immunosorbent assay< 0.156: no gluten excretion detected. NA: No adherence; ND: Not determined and excluded from analysis; –ve: Negative result; +ve: Positive result; DGP: Deamidated gliadin peptide; GIP: Gluten immunogenic peptides; ELISA: Enzyme-linked immunosorbent assay; PoCT: Point-of-care test.