Digestive issues can be uncomfortable and confusing. Two common conditions with gastrointestinal symptoms that affect many people are celiac disease and irritable bowel syndrome (IBS). While they can share some similar symptoms, including chronic diarrhea, they're actually quite different.
 

To help you better understand celiac disease and IBS and the difference between the two, we spoke with Annette Taylor, PhD, MS, FACMG, associate VP and strategic director of pharmacogenomics at Labcorp, and Jane Yang, MD, medical science director at Labcorp, about what causes these conditions, how to distinguish their symptoms and more.
 

What is celiac disease?

Celiac disease is an autoimmune, inflammatory disorder caused by an immune response to dietary gluten (a protein in wheat, rye and barley), which can happen in people with a specific genetic predisposition to the disease.

Celiac disease affects approximately 1% of people in the U.S., but less than 40% of people with the condition are diagnosed due to its wide range of symptoms (including both GI and non-GI) that can sometimes be confused with other health conditions.
 

What are the symptoms of celiac disease?

“A common misconception about celiac disease is that it’s only a GI disorder, but sometimes there are no GI symptoms,” says Dr. Taylor. “This is one of the reasons why celiac is underdiagnosed.”
 

GI symptoms of celiac disease may include:
 

• Diarrhea
• Abdominal pain
• Bloating
• Vomiting
• Weight loss

Non-GI symptoms of celiac disease can include:
 

• Rash (i.e., dermatitis herpetiformis)
• Iron deficiency anemia
• Osteoporosis
• Chronic fatigue
• Migraines

However, another common misconception is that celiac disease always has symptoms. “Many providers and patients aren’t aware of silent celiac disease, where the autoimmune and inflammatory response is happening in the patient’s body, but there are no symptoms apparent to the patient (or they may be subtle and not recognized by the patient as a sign of celiac disease),” explains Dr. Taylor. “Silent celiac disease is usually discovered by testing patients’ first-degree relatives who have the condition,” as there is at least a 1 in 10 chance of developing celiac if a parent, sibling or child already has it.
 

How is celiac disease diagnosed?

Celiac disease is diagnosed first by a blood test to detect celiac-specific antibodies, and if results are positive, often a small bowel biopsy (which involves taking a small tissue sample from the lining of the small intestine to check for signs of the condition) to confirm the diagnosis.
 

Blood tests, such as Labcorp OnDemand’s Celiac Disease Antibody Test, can help identify specific antibodies that develop in the body during the autoimmune reaction caused by celiac disease.
 

However, the Celiac Disease Antibody Test is only a first step toward diagnosis of the condition. If your results suggest celiac disease is possible or likely, talk to your healthcare provider about further testing, including a possible small bowel biopsy.
 

It is important to have been on a gluten-containing diet for at least two weeks when you have a celiac antibody test. The gluten-free diet decreases antibody levels, so a negative antibody test would not suggest a lack of celiac disease.
 

Celiac disease can develop at any age if you have a genetic predisposition to it. Genetic testing for celiac disease—which looks for specific variations in certain genes called HLA-DQA and HLA-DQB associated with the condition—can help provide clarity if other tests (i.e., antibody tests and small bowel biopsy) have negative or unclear results. Celiac genetic testing is useful if you are on a gluten-free diet, since negative results rule out celiac disease and positive results reveal susceptibility to celiac disease.
 

How can people with celiac disease ensure they’re getting adequate nutrition on a gluten-free diet?

Since there is no cure for celiac disease, managing the condition requires a lifelong gluten-free diet.
 

This diet plays a dual role: First, it helps heal the gut by stopping the immune response that damages the small intestine, reducing inflammation and allowing the intestinal lining to regenerate. Gut healing is essential to restore proper digestion and lower the risk of complications or secondary disorders that can happen in people with celiac disease (e.g., Type 1 diabetes, other autoimmune disorders). Second, a gluten-free diet is critical for maintaining nutritional health, as celiac-related damage can impair nutrient absorption, leading to deficiencies in iron, calcium, vitamin D, B12 and other micronutrients. Even after gluten is removed from your diet, nutritional challenges may persist if you’re lacking variety or rely heavily on processed gluten-free foods. Therefore, people with celiac disease must not only eliminate gluten but also focus on eating nutrient-dense, whole foods and possibly supplementing key nutrients to support both gut recovery and long-term health.

If you’re interested in learning more about your nutrition, Labcorp OnDemand’s Micronutrient Test measures your body’s levels of six essential vitamins and minerals (vitamin D, vitamin B12, folate, magnesium, iodine and zinc) and can help identify possible deficiencies. You can also explore Labcorp OnDemand’s full suite of nutrition and vitamin health tests to help you learn more about your body’s levels of iron, calcium and other key nutrients.
 

Is there a way to ensure your diet is truly gluten-free?

A strictly gluten-free diet is hard to maintain, and many people on the diet may not be symptom-free. Dr. Taylor recommends visiting the Celiac Disease Foundation’s website, which offers helpful guidance for gluten-free food substitutes, meal plans and more.
 

If you’re worried that you may have eaten gluten without realizing it, your healthcare provider can order a gluten stool test to help confirm.
 

What is irritable bowel syndrome (IBS) and how is IBS diagnosed?

IBS is a chronic condition that can cause various digestive symptoms, including diarrhea (IBS-D), constipation (IBS-C) or alternating diarrhea and constipation (IBS-M). Unlike celiac disease, IBS is not an autoimmune disease with a genetic predisposition. It’s estimated that IBS affects 10% to 15% of adults in the U.S.
 

What are the symptoms of IBS?

In addition to diarrhea and constipation, symptoms of IBS can include:
 

• Bloating
• Stomach pain that feels better after a bowel movement
• Changes in how often you have bowel movements
• Changes in the appearance of your stool
• Feeling like you haven’t completely emptied your bowels even after using the bathroom

Symptoms of IBS are chronic, meaning they happen at least one day per week within a period of three months, with an overall duration of at least six months.
 

How is IBS diagnosed?

There is no definitive test to diagnose IBS. “It is typically a diagnosis of exclusion,” says Dr. Yang. “This means your healthcare provider will likely rule out other possible causes of your symptoms to determine whether you have IBS.”
 

Your provider will likely begin with a complete medical history (including a discussion about the above symptoms), a physical exam and tests to rule out other related conditions (e.g., celiac disease, food allergy, inflammatory bowel disease).
 

Can celiac disease be confused with IBS?

Yes, celiac disease and IBS can sometimes be confused with one another. In fact, it’s estimated that between 5% and 15% of people diagnosed with celiac disease were originally diagnosed with IBS. This is largely due to overlapping GI symptoms, such as chronic diarrhea.
 

What is chronic diarrhea?

Diarrhea is mainly characterized by loose stools, though it can also be associated with symptoms such as:

• Abdominal pain and cramping
• Fever
• Nausea and vomiting
• Fatigue
• Urgency in bowel movements
• Blood in stool
• Increased number or volume of bowel movements
• Weight loss
• Malnutrition

The difference between chronic and acute diarrhea is the duration. Acute diarrhea, which is most often caused by infections, typically entails three or more loose stools per day for no more than two weeks and often resolves without treatment.

Diarrhea is considered chronic when it persists for longer than one month. It’s estimated that chronic diarrhea affects up to 5% of the population.

What causes chronic diarrhea and how is it treated?

Any process in the body that leads to increased fluid in the stool can cause chronic diarrhea. There is a wide range of possible causes of chronic diarrhea, from infections and systemic diseases to conditions that affect gut absorption and gut health. Both IBS and celiac disease are common causes of chronic diarrhea.

Treatment of chronic diarrhea depends on the underlying cause. It may involve fluid replacement, avoidance of certain foods, antibiotics or other targeted medications.

What should I do if I’m experiencing chronic diarrhea?

If you have chronic diarrhea, it’s important to talk to your healthcare provider, as they can help determine the underlying cause using a thorough medical history, physical exam and laboratory tests.

While celiac disease and IBS are common causes of chronic diarrhea, your provider can help you rule out other potential causes, such as inflammatory bowel disease (IBD) or certain infections.

“Navigating digestive issues can be challenging, but it’s important to remember that you’re not alone on this journey. Your healthcare team is there to support you every step of the way,” says Dr. Taylor. “Plus, with advancements in testing, we’re better equipped than ever to identify and manage these conditions.”

Think you might have celiac? Consider celiac disease antibody testing

As a first step in determining whether chronic diarrhea or other digestive health issues may be a sign of celiac disease, Labcorp OnDemand’s Celiac Disease Antibody Test can provide helpful insights.

Remember: This test is only a screening measure; if your results suggest celiac disease is possible or likely, talk to your healthcare provider about further testing and next steps.