How to Get Diagnosed With IBS: Tests, Criteria and Which Doctor

If you have recurring belly pain along with diarrhea, constipation or both, you may be wondering how to get diagnosed with IBS and where to start. Irritable bowel syndrome (IBS) is diagnosed mainly from your symptom pattern, history and a physical exam, backed by a few targeted tests for conditions that can look similar, such as celiac disease and inflammatory bowel disease (IBD). The criteria doctors use also changed in 2026 with the release of Rome V. This guide covers who to see, what the criteria say, which tests are typical, which symptoms need faster evaluation, and how to prepare.

How IBS is diagnosed, in short

The American College of Gastroenterology (ACG) IBS guideline suggests a positive diagnostic strategy over a strategy of exclusion. A clinician can name IBS once your symptoms fit the pattern and nothing points to another disease, without first testing for every possible cause. ACG's summary of the guideline describes this approach as a careful history, a physical exam and limited diagnostic testing, which can shorten the time to appropriate treatment. ACG's patient information on IBS notes that no single test proves someone has IBS, and that normal results do not mean the symptoms are imagined. Tests still matter, especially when diarrhea is part of the picture. If your main question is whether you have IBS or IBD, the guide to IBS vs IBD covers how the two differ.

Which doctor to see

For most people, the first stop is a primary care clinician such as a family medicine doctor, internist, nurse practitioner or physician assistant. In a 2026 interview, gastroenterologist Jan Tack said that a clinician confident in the symptom pattern, with no missed organic disease, can make the diagnosis. The lead author of the ACG guideline has described limited testing, including a complete blood count and a C-reactive protein test, as reasonable. A gastroenterologist, a physician who specializes in the digestive tract, usually becomes involved when there are warning signs, when the diagnosis is uncertain, or when symptoms do not improve with first treatments. Gastroenterologists also perform procedures such as an upper endoscopy with biopsy for celiac disease or a colonoscopy to look for colon cancer or IBD. Later, a registered dietitian may guide a low-FODMAP diet, and a GI psychologist may offer gut-directed psychotherapy. Insurance plans differ on whether a specialist visit needs a referral, so check your plan before booking.

The criteria doctors use

Clinicians define IBS with the Rome criteria, and the current version is Rome V. The Rome Foundation lists June 1, 2026 as the ship date for Rome V, and its bowel disorders chapter was published by Corsetti and colleagues in Gastroenterology. For IBS, Rome V re-includes "discomfort" alongside pain and lowers the threshold to 3 days per month, replacing the weekly rule in Rome IV. It also specifies that IBS pain cannot be continuous, and Tack explains that pain should not be exclusively or mainly tied to the menstrual period, which helps avoid missing endometriosis.

Rome V separates research diagnostic criteria from clinical criteria. Research criteria keep fixed thresholds for trials, while Tack says the clinical criteria omit frequency and duration thresholds and treat bothersome symptoms as sufficient. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) diagnosis page, last reviewed in 2017, still describes the older weekly rule. In a UK registry of people who report having IBS, 70% met Rome V criteria compared with 59% under Rome IV, though the Rome V group had milder symptoms and a less stable diagnosis over follow-up. Rome V is broader, and researchers are still studying what that means for care.

Tests that rule out other conditions

For suspected IBS with diarrhea, the ACG guideline suggests celiac serology and fecal calprotectin, and its lead author has said ACG also recommends checking C-reactive protein (CRP) and fecal lactoferrin. The American Gastroenterological Association (AGA) laboratory guideline suggests calprotectin or lactoferrin but suggests against CRP to screen for IBD. AGA also recommends celiac testing with IgA tissue transglutaminase plus a second test if IgA is low, recommends Giardia testing, suggests bile acid diarrhea testing, and makes no recommendation for current IBS blood panels. Keep eating gluten until celiac testing is done, because a gluten-free diet can affect test results.

Test	What it looks for	When it is typically ordered
Celiac blood test with IgA level	Celiac disease	Suspected IBS with diarrhea, per ACG and AGA
Fecal calprotectin or lactoferrin	Bowel inflammation suggesting IBD	Suspected IBS with diarrhea, per ACG and AGA
C-reactive protein	Inflammation in the blood	Included by ACG; AGA suggests against it
Complete blood count	Anemia	Limited testing described by ACG's lead author
Giardia stool test	A common intestinal parasite	Chronic diarrhea, per AGA
Bile acid diarrhea test	Bile acid malabsorption	Chronic diarrhea, per AGA
Colonoscopy	Colon cancer, IBD	Warning signs or screening age

ACG recommends against routine colonoscopy in people with IBS symptoms under 45 who have no warning signs. Routine screening still applies: the US Preventive Services Task Force recommends colorectal cancer screening for adults aged 45 to 75.

Red flags that change the plan

Some symptoms call for prompt evaluation for another condition before anyone settles on IBS. NIDDK lists anemia, rectal bleeding, black and tarry stools, and weight loss as signs that may point to a different health problem. The ACG guideline summary adds unintentional weight loss, older age at symptom onset, and a family history of IBD, colon cancer or other significant digestive disease. A review by Lacy and Patel also names bowel movements at night, a lump that can be felt in the abdomen, and age over 50 without prior colon cancer screening, and ACG's patient page lists low iron levels and new symptoms later in life. Call your clinician soon if any of these apply, even if the symptom comes and goes. Doctors also ask about celiac disease, colon cancer and IBD in relatives when deciding which tests to order.

IBS subtypes and why they matter

IBS subtypes are based on stool form, scored on the Bristol Stool Form Scale from type 1, hard lumps, to type 7, watery. Under Rome IV, IBS with constipation (IBS-C) means more than 25% of bowel movements are Bristol type 1 or 2, and IBS with diarrhea (IBS-D) means more than 25% are type 6 or 7. Meeting both is IBS with mixed bowel habits (IBS-M), and there is also an unsubtyped group, IBS-U. These cutoffs come from Rome IV, so ask your clinician whether they still apply under Rome V. The Bristol stool chart guide explains how to score each stool.

Subtype shapes the workup and treatment. The ACG lead author noted that diagnostic testing generally depends on the subtype, and most tests above are aimed at IBS-D. Lacy and Patel describe subtyping as a way to focus treatment on the most bothersome symptom and recommend a careful rectal exam in people with constipation to check for pelvic floor dyssynergia. After diagnosis, the overview of evidence-based IBS treatment options covers the next steps.

How to prepare for the diagnosis visit

A symptom diary gives your clinician the pattern that the criteria and subtype rules rely on. Lacy and Patel suggest a 14-day bowel diary to classify subtypes accurately, so aim for at least two weeks of entries. Each day, record:

• days with pain or discomfort, and whether it changed with a bowel movement
• each stool's Bristol type, the number of bowel movements, and any at night
• meals, medicines, and your menstrual cycle if you have periods

Note any blood, black stools or unplanned weight loss separately. Write down which relatives have had celiac disease, IBD or colon cancer, and keep eating gluten until testing is complete. At the visit, ask which criteria the clinician is using, which tests fit your symptoms, and what subtype your diary suggests.

Getting diagnosed with IBS usually starts in primary care with a focused set of tests, with a referral to a gastroenterologist if warning signs appear or the picture stays unclear. Rome V has widened who qualifies while adding checks that keep continuous pain and period-related pain from being labeled IBS too quickly. A few weeks of careful records and an accurate family history give your clinician what they need to reach a confident diagnosis.