Gluten Immunogenic Peptide tests for coeliac patients

The role of immunogenic peptides in monitoring adherence to a gluten-free diet in coeliac disease

One of the most persistent challenges for clinicians managing coeliac disease is knowing whether patients are truly adhering to a gluten-free diet. In this blog series, Ángel Cebolla, CEO of Biomedal SL, explores how a Gluten Immunogenic Peptide (GIP) test is a practical tool to assess patients, giving clinicians clearer information about their diets.

Why adherence matters in coeliac disease

Coeliac disease affects approximately 1 per cent of the population in the UK,¹ making it one of the most common autoimmune conditions seen in clinical practice. The pathophysiology is well understood: ingestion of gluten triggers an immune-mediated inflammatory response that damages the small intestinal mucosa. Over time, this can result in villous atrophy, a reduced capacity for absorption and a range of complications including nutritional deficiencies and osteoporosis.

At present, a strict gluten-free diet remains the only effective treatment. Careful adherence can help to reduce intestinal inflammation and allow mucosal recovery in coeliac patients. However, even small amounts of gluten can trigger immune activation and cause mucosal injury. This is why monitoring dietary adherence remains such an important part of long-term management.

Non-adherence to a gluten-free diet is common in coeliac patients

In the real world, perfect adherence is difficult to achieve. Across published studies, non-adherence rates range from 8 per cent to as high as 70 per cent, depending on how it is measured. Most individuals consume over 1,000 meals per year, many outside their own homes. Eating out, cross-contamination in shared kitchens and hidden ingredients can easily result in coeliac patients eating gluten unintentionally; even those who are highly motivated may be accidentally exposed. As a result, many continue to show persistent villous atrophy despite reporting strict dietary adherence. Research has found that 65 per cent of treated adults still do not have complete normalisation of the intestinal mucosa, showing a clear need for continual monitoring.² However, traditional monitoring techniques – including questionnaires, symptomology, serology and biopsy – have limitations that can make assessing adherence challenging.

Why traditional monitoring tools fall short

Dietary questionnaires

Dietary questionnaires are widely used during follow-up visits, however, they are inherently subjective and time consuming. Patients may unknowingly underestimate their gluten intake, particularly when cross-contamination is involved and they are not aware of exposure. Studies using GIP tests have shown that many patients who report strict adherence still test positive for gluten exposure,³ highlighting the limitations of relying exclusively on self-reported dietary history.

Symptomology

Clinical symptoms are often unreliable indicators of exposure. A significant proportion of individuals remain asymptomatic even when intestinal damage is present. Interestingly, some research has shown a clinical paradox: patients with the highest level of gluten exposure sometimes report fewer symptoms. In one study, up to 80 per cent of patients with poor adherence to a gluten-free diet had confirmed villous atrophy.⁴

Serology

Serological markers such as anti-tissue transglutaminase antibodies (anti-tTG) are useful at diagnosis, but they are less reliable for long-term monitoring. Serology has a low correlation with the presence of symptoms and the state of the mucosa, ⁴ it fails to detect the time of gluten intake, and requires a blood draw.

Biopsy

Duodenal biopsy remains the gold standard for assessing mucosal status, but it is invasive and resource intensive, so is not suitable for frequent monitoring. Importantly, biopsy also detects damage that has already occurred rather than identifying recent harm triggered by gluten exposure. It would be far more useful for clinicians to be able to detect dietary non-adherence before damage occurs.

How GIP testing works in practice (urine vs stool)

GIP testing provides an objective measurement of recent gluten exposure, by highlighting the fragments of gluten that resist digestion and remain detectable in biological samples after ingestion. GIP tests can detect these peptides in both urine and stool samples. Urine testing indicates almost immediate exposure; GIP is detectable from one to six hours after ingestion, peaks at between six and nine hours, and clears within 36 hours. Stool testing offers a longer window of detection from approximately 24 hours after ingestion, peaking at two days, and the GIP can remain detectable for up to a week, making it ideal for identifying exposure over a longer period.

What studies show about hidden gluten exposure

Over the past decade, a growing body of research has explored the clinical value of GIP detection in monitoring adherence to a gluten-free diet. One consistent finding is that GIP positivity correlates strongly with persistent villous atrophy, with patients who tested positive significantly more likely to demonstrate mucosal damage compared to those who tested negative.⁴ The DELIAC study found that many patients who claim to adhere to a gluten-free diet still showed measurable gluten exposure with GIP testing.⁵ Other studies have also shown that GIP detection appears to correlate with mucosal status more closely than serology, providing a more effective objective measure.⁶

The future of coeliac disease monitoring

Monitoring coeliac disease requires more than symptom assessment and routine blood tests; GIP detection provides direct evidence of gluten ingestion and may help clinicians to identify ongoing exposure that would otherwise remain hidden. Conversely, if symptoms persist following dietary intervention, GIP detection should be used to determine whether these symptoms can be attribute to causes other than gluten ingestion. Integrating this testing into clinical practice may help to improve dietary counselling, identify inadvertent exposure and ultimately protect patients’ intestinal health. As our understanding of the value of GIP testing continues to grow, objective monitoring of gluten exposure is likely to become an increasingly important part of coeliac disease management.

Read Ángel’s next blog to find out how GIP testing can be implemented into your clinical pathways.

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1. Coeliac UK. About Coeliac Disease. Accessed 12^th of March 2026. https://www.coeliac.org.uk/about-coeliac-disease/
2. Lanzini A, et al. (2009) Complete recovery of intestinal mucosa occurs very rarely in adult coeliac patients despite adherence to gluten-free diet. Aliment Pharmacol Ther. 29(12):1299-1308. doi:10.1111/j.1365-2036.2009.03992.x
3. Stefanolo JP, et al. (2021) Real-World Gluten Exposure in Patients With Celiac Disease on Gluten-Free Diets, Determined From Gliadin Immunogenic Peptides in Urine and Fecal Samples. Clin Gastroenterol Hepatol. 19(3):484-491.e1. doi:10.1016/j.cgh.2020.03.038
4. Ruiz-Carnicer, Á et al. (2020) Negative predictive value of the repeated absence of gluten immunogenic peptides in the urine of treated celiac patients in predicting mucosal healing: new proposals for follow-up in celiac disease. 112(5):1240-1251.
5. Comino I, et al. (2016) Fecal Gluten Peptides Reveal Limitations of Serological Tests and Food Questionnaires for Monitoring Gluten-Free Diet in Celiac Disease Patients. Am J Gastroenterol. 111(10):1456-1465. doi:10.1038/ajg.2016.439
6. Moreno MDL, et al. (2017). Detection of gluten immunogenic peptides in the urine of patients with coeliac disease reveals transgressions in the gluten-free diet and incomplete mucosal healing. 66:250-257.