What Kind of Doctor for IBS? Colonoscopy and Blood Tests

You have had stomach pain, bloating or diarrhea for months. Now you wonder who to see, and whether you need a colonoscopy. Your test reports can go in a folder or in Sam's Health Vault, which reads values like CRP and hemoglobin from lab reports once you consent.

This post covers who does what, which blood and stool tests are used, and when a colonoscopy comes in. What to write down before the visit is in IBS and your doctor: what to write down. What Sam keeps for IBS, and what it does not, is on the IBS page.

What kind of doctor treats IBS?

Most people start with their GP or primary care doctor. The NHS says a GP may ask about your symptoms, feel your tummy and arrange tests. It says you will not usually need hospital tests unless the GP is not sure what the problem is. The American College of Gastroenterology (ACG) says most people can be diagnosed from history, an exam and limited testing.

A gastroenterologist is a specialist in stomach and bowel conditions. You may see one when tests need an endoscopy, when your GP is not sure what the problem is, or when another bowel condition is suspected. If a celiac blood test is positive, for example, the NHS says the GP will refer you to a gastroenterologist.

The German S3 guideline splits the work like this. A GP can do the basic tests. The endoscopies needed to confirm the diagnosis are mostly done by gastroenterologists. Either one, or both, can give you the diagnosis.

For women, that guideline adds a gynecological check to the basic work-up. Gynecological causes such as ovarian cysts can cause similar symptoms. If your pain follows your period, endometriosis: prepare your symptoms for the doctor helps you get ready. For how to log gut symptoms across a cycle, see IBS before your period.

The criteria doctors use to classify IBS (Rome IV, and Rome V since 2026) are covered in the what-to-write-down post. They are a tool for doctors, not a test to run on yourself. Missing a criterion is not an all-clear.

Which blood and stool tests rule out other causes?

There is no test that proves IBS. The tests look for conditions that can cause the same symptoms. The NHS names a blood test for celiac disease and stool tests for infection and inflammatory bowel disease. The ACG's patient page adds blood work for inflammation.

The American Gastroenterological Association (AGA) has a guideline for adults with watery diarrhea lasting at least four weeks. Its main points:

• It recommends a celiac blood test (IgA tissue transglutaminase), plus a second test if IgA levels are low.
• It suggests fecal calprotectin or fecal lactoferrin, two stool markers, to screen for inflammatory bowel disease.
• It suggests against CRP or ESR, two blood markers of inflammation, for that purpose.
• It recommends a stool test for Giardia, a gut parasite.
• It makes no recommendation for currently available blood tests to diagnose IBS.

The German S3 guideline lists basic bloods with celiac antibodies. It adds stool tests for infections and for inflammation markers such as calprotectin. It does not currently recommend biomarker tests as proof of IBS. It advises against gut flora (microbiome) stool tests.

Three points help when you go through the results with your doctor.

• Calprotectin: in the German guideline, clearly raised levels point quite reliably to a process in the gut, usually inflammation. Inflammation only in the small bowel, as in some Crohn's disease, shows up in only about 70 percent of cases. A normal result does not rule that out.
• Celiac test: the NHS says to keep eating gluten for the blood test. Avoiding it can make the result inaccurate. Talk to your doctor before you cut gluten out.
• Inflammation and anemia: in the German guideline, these and other relevant lab changes rule out IBS as a working diagnosis until explained.

These are tests your doctor reads with your history and exam, not results to judge on your own. A normal value is not an all-clear.

You can photograph a lab report or add the PDF to the Health Vault in Sam. Once you consent, Sam reads the values and matches about 33 of them to a fixed name. They include CRP, hemoglobin and white blood cells. Calprotectin and celiac antibodies are not among them; those rows stay as printed. Sam can also file a row under the wrong value name, for example a "fecal hemoglobin" row under hemoglobin. Sam shows whether a value is above or below the range your lab printed on the report. When a report prints separate ranges for women and men, Sam keeps only the first one. Check the values against the original report.

Do you need a colonoscopy for IBS?

It depends on your symptoms, your age and which guideline your doctor follows. According to the ACG's own summary of its 2021 guideline, it recommends against routine colonoscopy for people with IBS symptoms under 45 who have no warning signs. The summary's examples are unintentional weight loss and symptoms that start at an older age. A family history of inflammatory bowel disease, colon cancer or other significant gut disease counts too. The ACG's patient page also lists rectal bleeding and low iron levels, and says a colonoscopy may be needed when such signs are present. Blood in your stool needs a doctor today at any age. The other signs in the section "Which signs need a doctor today or an emergency call?" do not wait for this decision either.

The German S3 guideline goes further. After the basic tests, it usually adds two scopes. One is a colonoscopy reaching the end of the small bowel. The other is a gastroscopy with biopsies from the duodenum. When diarrhea is a main symptom, it asks for a full work-up. That includes stool tests for infection and colon biopsies from several points.

Its reason: some conditions cannot be told apart from IBS by symptoms alone. It names, among others, inflammatory bowel disease, microscopic colitis and celiac disease. If symptoms began less than a year ago, it adds bowel cancer. It says the absence of warning signs does not reliably rule these out. Microscopic colitis, for example, can only be found with biopsies. In a review of 26 studies, it was behind almost one in ten cases of apparently typical IBS with diarrhea.

The German guideline also leaves room. With typical IBS symptoms and no diarrhea, a doctor may skip the full work-up after normal basic tests. Treatment can then be tried for up to two months. IBS is then not yet diagnosed. If a sign from "Which signs need a doctor today or an emergency call?" appears in that time, do not wait. Both approaches are medical judgments, not rules to apply yourself. Your doctor decides with you whether and when you need a colonoscopy. You can ask why one is or is not planned.

Can a colonoscopy show IBS?

No. The German guideline says IBS symptoms are real and involve physical changes, but routine tests cannot show them. A colonoscopy looks for other causes, such as inflammation or bowel cancer, and biopsies look for microscopic colitis.

A normal result fits IBS but does not prove it on its own. Your history and the pattern of your symptoms also have to fit.

Once IBS has been carefully diagnosed, the diagnosis usually holds. In studies with 2 to 30 years of follow-up, it stayed the same in more than 95 percent of people. So the German guideline advises doctors not to repeat tests unless something new comes up. Whether anything is checked again is for your doctor to decide; tell them about new or changed symptoms. The signs under "Which signs need a doctor today or an emergency call?" always need a doctor, diagnosis or not.

How is IBS different from IBD?

Inflammatory bowel disease (IBD) is not the same as IBS, even though some symptoms are similar, the NHS says. It lists three types: Crohn's disease, ulcerative colitis and microscopic colitis. Ulcerative colitis affects the rectum and large bowel; Crohn's disease can affect any part of the gut, from mouth to bottom.

The difference shows in test results more than in symptoms. The German S3 guideline cites meta-analyses on this. In them, about a third of people with IBD had full IBS-type symptoms while their inflammation was quiet. To diagnose Crohn's disease, the NHS describes blood and stool tests from the GP. Hospital tests follow, such as a colonoscopy, biopsies and scans.

Which condition you have is for your doctor to decide from the results.

How do you prepare for the gastroenterology appointment?

Bring your referral letter if you have one, your lab results and earlier reports from scopes or scans. Add a list of your medicines. For the rest, the doctor appointment checklist for a chronic condition helps. Questions you can ask:

• Which tests are planned, and what are they looking for?
• Do I need a colonoscopy or a gastroscopy, and will you take biopsies?
• What happens if everything comes back normal?
• When and how will I get the results?

If symptoms get worse while you wait, or a sign from the next section appears, do not wait for the appointment.

Which signs need a doctor today or an emergency call?

These signs need an urgent appointment today, even if you already have an IBS diagnosis:

• Blood in your stool, bleeding from your bottom or bloody diarrhea.
• Losing a lot of weight for no reason.
• A hard lump or swelling in your tummy.
• Symptoms that suddenly get much worse.
• Shortness of breath with palpitations and paler skin than usual.

Outside practice hours, use your local out-of-hours service (NHS 111 in the UK).

Also get these checked before anyone calls it IBS, and if you already have an IBS diagnosis:

• Fever.
• Anemia on a blood test.
• Unusual paleness.
• Symptoms that keep getting worse.
• Diarrhea that wakes you at night.
• Symptoms that first started after age 50.
• Smaller unintended weight loss.
• Bowel cancer, inflammatory bowel disease or celiac disease in your family.

These lists are not complete and are not a self-test. New or lasting bowel symptoms are worth a doctor's visit even without any of these signs. The first list follows the NHS, which advises an urgent GP appointment or NHS 111 for these signs. IQWiG, the German health information institute, says blood in the stool should always be checked by a doctor. The second list draws on the German S3 guideline, IQWiG and a 2023 American Family Physician summary of the AGA guideline.

Call your local emergency number (112 in the EU, 999 in the UK, 911 in the US) for stomach pain that starts suddenly and is severe. The same applies to a lot of blood from your bottom, black sticky stool, or vomiting blood or vomit that looks green or like ground coffee. Not being able to pass stool or wind at all, struggling to breathe, and sudden chest pain or pressure also need an emergency call. Do not wait for it to pass.

Keep your lab reports and gut days in Sam and bring them along

Your lab reports, letters and gut days come with you in one place, not spread across folders and memory.

• Instead of a folder: lab reports, colonoscopy reports and doctor's letters go into the Health Vault as photos or PDFs.
• Instead of retyping: once you consent, Sam reads values such as CRP, hemoglobin and white blood cells from a lab report. You check them before saving.
• Instead of memory: the symptom diary keeps abdominal pain, bloating, diarrhea or constipation per day, as mild, moderate or severe.

Sam does not recognize calprotectin or celiac antibodies as values of their own; those rows are kept as printed. What a result means for you is a question for your doctor. More on the IBS page.

Try Sam for free

Sam is a wellness companion, not a medical device. The app does not diagnose, treat, cure or prevent any condition or health state. Always consult qualified professionals for medical decisions.

Related reading

• IBS and your doctor: what to write down
• Doctor appointment checklist for a chronic condition
• IBS before your period: what to log across your cycle
• Endometriosis: prepare your symptoms for the doctor
• Symptom diary: paper template or app?

Sources

Updated: October 2026

• NHS: IBS - Diagnosis and IBS - Symptoms (reviewed 17 March 2025)
• NHS: Coeliac disease - Diagnosis (reviewed 31 March 2023), Inflammatory bowel disease (reviewed 11 September 2026) and Crohn's disease - Diagnosis (reviewed 14 April 2025)
• NHS: Stomach ache (reviewed 20 October 2026) and Chest pain (reviewed 8 August 2023)
• American College of Gastroenterology: ACG's First Clinical Guideline on Management of Irritable Bowel Syndrome (PDF), ACG Magazine 2021, summary of the ACG guideline in The American Journal of Gastroenterology; the guideline itself was not opened for this post
• American College of Gastroenterology: Irritable Bowel Syndrome (patient page, updated February 2026)
• AGA Institute: Laboratory Evaluation of Functional Diarrhea and Diarrhea-Predominant Irritable Bowel Syndrome in Adults. Smalley W et al., 11 July 2019
• Arnold MJ: Practice Guidelines: Irritable Bowel Syndrome. Am Fam Physician 2023;108(5):527-529, Table 1 (summary of the AGA guideline)
• DGVS and DGNM: S3 guideline on irritable bowel syndrome, 2021 update (PDF). Layer P et al., Z Gastroenterol 2021;59:1323-1415, AWMF 021-016, as of June 2021: recommendations 3-1, 3-2, 3-4, 3-6A, 3-6B, 3-7, 3-8, 3-9, 3-11, tables 3-1 to 3-4, preface to part IV (care coordination); being updated per DGVS (in German)
• IQWiG (gesundheitsinformation.de): Reizdarmsyndrom (updated 22 February 2023, in German)