How Is Ulcerative Colitis Diagnosed?

Ulcerative colitis is an inflammatory bowel disease (IBD) that causes irritation and sores in the lining of the colon and rectum (the last sections of the large intestine). The most common symptoms of ulcerative colitis are diarrhea (with or without blood) and abdominal pain. 

A gastroenterologist is a physician who specializes in bowel disease. They use endoscopic tests and biopsies to definitively diagnose ulcerative colitis. Endoscopic tests include a colonoscopy or flexible sigmoidoscopy.

This article reviews the steps and tests healthcare providers use to diagnose and stage ulcerative colitis.

Middle-aged man sits on sofa holding stomach in pain

supersizer / Getty Images

Medical History

The first step toward a diagnosis is a medical history. Your healthcare provider will ask about symptoms, timing, family history, and past medical conditions. 

Some questions involve bowel movement (pooping) habits and your sexual history. While these questions may feel intrusive, your answers provide clues to help your provider rule out similar diseases.

Questions they may ask include:

  • Do you have diarrhea? 
  • Do you have pain or cramping in your abdomen?
  • Do you have rectal pain? (The rectum is the last part of the intestines, close to where stool exits the body) 
  • Do you ever have constipation?
  • How many times a day do you have diarrhea? 
  • How long have you had diarrhea?
  • Did these symptoms come on suddenly or over time?
  • Have you ever had diarrhea that wakes you up at night?
  • Do you have blood or pus in your stool?
  • Have you had strong urges (urgency) to have bowel movements after you’ve already emptied your bowels? 
  • How frequently do you experience urgency but cannot have a bowel movement? 
  • Have you traveled out of the country recently?
  • When is the last time you took antibiotics?
  • Could you possibly have a sexually transmitted infection or disease (STI or STD)?
  • Have you ever had radiation therapy?
  • What medications do you take?
  • Do you take over-the-counter pain medications such as Advil or Motrin (ibuprofen), or Bayer (aspirin)?
  • Have you recently stopped smoking? 
  • Do you have any problems with your immune system? 

Diarrhea (with and without blood) and abdominal pain are the two most common symptoms of ulcerative colitis. Onset is typically gradual and gets worse over time. Your healthcare provider may suspect ulcerative colitis if you have chronic diarrhea that lasts over four weeks.

Physical Examination

The next step is typically a physical exam. During an examination, your provider will look for things such as a fever, low blood pressure, increased heart rate, abdominal tenderness, and malnutrition. They may also perform a rectal exam to look for blood in your stool.

Normal physical exam findings do not rule out ulcerative colitis. 

Lab Tests

While lab tests won’t diagnose ulcerative colitis, they provide essential information and can help rule out similar diseases.

Blood tests may include:

  • Complete blood count (CBC): A CBC checks your red and white blood cells. It provides clues about potential infections and blood loss.
  • Chemistry panel: A chemistry panel (chem 8 or chem 20) provides information about your electrolyte levels and whether or not you’re dehydrated. 
  • C-reactive protein (CRP) test: C-reactive protein is a protein made in the liver. A high CRP level indicates excess inflammation in the body, a hallmark of ulcerative colitis.
  • Albumin: Low blood levels of the protein albumin may indicate malnutrition.
  • Erythrocyte sedimentation rate (ESR): Like CRP, an ESR also detects inflammation.
  • Polymerase chain reaction (PCR): A PCR detects the DNA or RNA (genetic makeup) of certain pathogens (things that cause disease).
  • P-ANCA and ASCA: The perinuclear antineutrophil cytoplasmic antibodies (P-ANCA) and anti-saccharomyces cerevisiae antibodies (ASCA) tests look for specific antibodies and antigens to help differentiate ulcerative colitis from other related conditions such as Crohn’s disease.

Stool samples can detect blood, infections, and fecal calprotectin levels (provide clues about inflammation in the digestive tract).

Depending on your symptoms and sexual activity, your provider may check your blood or genital fluid for sexually transmitted infections or diseases (STIs or STDs).


A colonoscopy is an endoscopic exam that visualizes the large intestine. To conduct the exam, your gastroenterologist inserts a small tube with a video camera into your rectum. This allows them to look for irritation, sores, or scar tissue on the lining of the rectum and colon.

Flexible Sigmoidoscopy 

A flexible sigmoidoscopy is an endoscopic exam similar to a colonoscopy. The difference is that the tube does not go as far into the intestines. It may replace a colonoscopy if you are severely sick or at risk for a potential complication called a toxic megacolon.


A biopsy is a sample of tissue sent to the lab for testing. During an endoscopy, the gastroenterologist will collect an intestinal sample for biopsy from several different areas of the colon.

The only way to definitively diagnose ulcerative colitis is through endoscopy tests that include biopsies.


An ulcerative colitis diagnosis does not require imaging tests such as X-rays, computerized tomography (CT), or a barium enema. Your healthcare provider may order these tests to help rule out other diseases. However, normal imaging results do not rule out or confirm ulcerative colitis.

Diagnostic Criteria

The diagnostic criteria for ulcerative colitis includes a combination of factors listed below:

  • Chronic diarrhea for more than four weeks
  • Endoscopic findings (such as inflammation, sores, bleeding, vascular pattern, scar tissue)
  • Histology (biopsy findings)
  • Exclusion of other causes of colitis by history, lab work, and biopsy
  • After diagnosis, your healthcare provider will also stage ulcerative colitis to note the extent and severity of the disease. This helps when planning treatment. 

The Mayo Score

There are several different scoring systems that healthcare providers use to stage ulcerative colitis. The Mayo score is one of the most popular systems.

The Mayo score takes into account stool frequency, rectal bleeding, endoscopy findings, and the provider's global assessment. Global assessment refers to your quality of life, discomfort, sense of well-being, and disability.

Regardless of which system a healthcare provider uses, they typically grade ulcerative from remission to severe as follows:

  • Remission: Free of symptoms
  • Mild: Fewer than four stools per day, with or without blood; no signs of systemic toxicity or inflammation; pain is minimal
  • Moderate: Frequent bloody diarrhea; more than four episodes per day; mild anemia, not requiring blood transfusion; minimal signs of toxicity, adequate nutrition, and mild weight loss
  • Severe: More than six episodes of bloody diarrhea per day; symptoms may include extreme pain, fever, elevated heart rate, anemia, malnutrition, weight loss, and an increased ESR

Healthcare providers also classify ulcerative colitis by the area of irritation and how far it spreads:

  • Ulcerative proctitis: Inflammation in the rectum
  • Proctosigmoiditis: Irritation in the rectum and sigmoid colon (lower end of the large intestines)
  • Left-sided colitis: The inflammation extends up the color to the left side of the body around the spleen
  • Pancolitis: Inflammation in the whole colon

Screening for Related Conditions 

A differential diagnosis means to rule out similar diseases. Crohn’s disease is the most commonly mistaken for ulcerative colitis. They are both inflammatory bowel diseases (IBDs). However, they occur in different areas of the digestive tract.

Crohn’s disease can affect any part of the digestive tract, while ulcerative colitis affects the colon and the rectum. These are the areas closest to the anus, where stool exits the body.

Healthcare providers will consider the following health conditions for those who have abdominal pain and bloody diarrhea:

Healthcare providers exclude similar health conditions through a medical history, endoscopy, lab tests, and biopsies. 

A raised fecal calprotectin narrows the focus to IBD (ulcerative colitis or Crohn’s disease), but it can’t differentiate ulcerative colitis from Crohn's because it does not show the location of the inflammation. 

Your provider may order the following lab tests to help differentiate ulcerative colitis from Crohn’s.

  • P-ANCA: Sixty to 70% of those with ulcerative colitis have P-ANCA antibodies. But, P-ANCA can be present in some with Crohn’s. 
  • ASCA: ASCAs are found in both types of IBD, but are more prevalent in Crohn’s disease.

Comorbid Conditions

Comorbidities are other chronic conditions that may occur with a disease. Your provider may also screen you for these common comorbidities:  

A Quick Review

Ulcerative colitis is an inflammatory bowel disease (IBD) that causes irritation and sores in the lining of the colon and rectum. Diarrhea (with or without blood) and abdominal pain are the most common symptoms.

A gastroenterologist will use an endoscopy (colonoscopy or sigmoid flexible sigmoidoscopy) and biopsies to make a definitive diagnosis. They will also order tests and gather information to rule out similar diseases and screen for comorbidities. 

Was this page helpful?
5 Sources uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Lynch WD, Hsu R. Ulcerative colitis. In: StatPearls. StatPearls Publishing; 2022.

  2. Peppercorn MA, Kane SV. Clinical manifestations, diagnosis, and prognosis of ulcerative colitis in adults. In: Post TW. UpToDate. UpToDate; 2022.

  3. Ungaro R, Mehandru S, Allen PB, Peyrin-Biroulet L, Colombel JF. Ulcerative colitis. The Lancet. 2017;389(10080):1756-1770. doi:10.1016/s0140-6736(16)32126-2 

  4. Pabla BS, Schwartz DA. Assessing severity of disease in patients with ulcerative colitis. Gastroenterol Clin North Am. 2020;49(4):671-688. doi:10.1016/j.gtc.2020.08.003

  5. Centers for Disease Control and Prevention. Inflammatory bowel disease (IBD) comorbidities

Related Articles