Ulcerative colitis is a type of inflammatory bowel disease (IBD) that causes inflammation and sores in the lining of the colon and rectum. The most common symptoms are diarrhea—sometimes with blood—and abdominal pain. A gastroenterologist, a doctor who specializes in bowel disorders, is typically the one who diagnoses ulcerative colitis using a combination of medical history, physical exams, lab tests, and endoscopic procedures such as colonoscopy or flexible sigmoidoscopy.

Step 1: Medical History

The diagnostic process begins with a thorough review of your medical history. Your healthcare provider will ask about your symptoms, how long they’ve lasted, your family history, and any previous medical issues. You may be asked about your bowel habits and sexual health. Though some questions might feel personal, they help rule out other potential causes.

Common questions include:

  • Do you experience abdominal pain, cramping, or rectal pain?

  • Have you had blood or mucus in your stool?

  • Are you experiencing frequent diarrhea or nighttime bowel movements?

  • Have you noticed urgency to go even after emptying your bowels?

  • Do you take over-the-counter medications like ibuprofen or aspirin?

  • Have you traveled recently or stopped smoking?

  • Are there any autoimmune conditions or infections in your health history?

Chronic diarrhea lasting more than four weeks is a strong indicator that ulcerative colitis may be present.

Step 2: Physical Examination

Next, your provider will perform a physical exam to look for signs of systemic illness, such as fever, low blood pressure, rapid heart rate, and abdominal tenderness. They may also conduct a rectal exam to check for visible blood in the stool. However, even a normal physical exam doesn’t rule out ulcerative colitis.

Step 3: Lab Tests

Lab tests alone cannot confirm ulcerative colitis, but they are helpful in assessing inflammation and ruling out other conditions. These may include:

  • Albumin: Low levels can indicate poor nutrition.

  • C-reactive protein (CRP): Elevated levels suggest active inflammation.

  • Electrolyte panel: Checks for dehydration or imbalance.

  • Complete blood count (CBC): Evaluates red and white blood cells to detect anemia or infection.

  • Erythrocyte sedimentation rate (ESR): Another marker of inflammation.

  • Antibody tests (P-ANCA and ASCA): Help distinguish ulcerative colitis from Crohn's disease.

  • PCR test: Identifies infectious agents through their genetic material.

  • Stool tests: Detect infections, blood, and levels of fecal calprotectin—a marker of inflammation.

Your healthcare provider may also order blood or fluid tests to rule out sexually transmitted infections (STIs) depending on your symptoms.

Step 4: Endoscopic Tests

Colonoscopy

This procedure uses a flexible tube with a camera inserted into the rectum to view the entire colon. It allows doctors to examine the intestinal lining for signs of inflammation, ulcers, or scar tissue.

Flexible Sigmoidoscopy

Similar to a colonoscopy, but only examines the lower part of the colon. It may be recommended if a full colonoscopy is unsafe or if there’s a risk of complications such as toxic megacolon.

Step 5: Biopsy

During an endoscopy, your doctor may take small samples of tissue from the colon for lab analysis. A biopsy is essential for a definitive diagnosis and to confirm the presence of inflammation consistent with ulcerative colitis.

Step 6: Imaging (If Needed)

Although imaging is not required to diagnose ulcerative colitis, scans such as X-rays, CT scans, or a barium enema might be used to rule out other diseases. Normal imaging results do not eliminate the possibility of ulcerative colitis.

Diagnostic Criteria for Ulcerative Colitis

To diagnose ulcerative colitis, providers evaluate:

  • Chronic diarrhea lasting over four weeks

  • Findings from endoscopy (such as inflammation or ulcers)

  • Biopsy results

  • Exclusion of other causes through lab work and history

Staging and Classifying the Disease

Healthcare providers use staging systems to assess the severity and extent of the disease. One widely used system is the Mayo Score, which evaluates:

  • Stool frequency

  • Presence of rectal bleeding

  • Endoscopic findings

  • Overall health assessment and impact on quality of life

Severity Stages:

  • Remission: No symptoms

  • Mild: Fewer than four bowel movements daily, with or without blood; minimal pain

  • Moderate: Frequent bloody stools; mild anemia; minimal weight loss

  • Severe: More than six bloody bowel movements daily; severe pain, fever, malnutrition, significant weight loss, and signs of systemic illness

Disease Location Classifications:

  • Ulcerative proctitis: Limited to the rectum

  • Proctosigmoiditis: Inflammation in the rectum and lower colon

  • Left-sided colitis: Affects the colon up to the splenic flexure

  • Pancolitis: Involves the entire colon

Screening for Related Conditions

Since other diseases can resemble ulcerative colitis, healthcare providers will rule out:

  • Crohn’s disease

  • Gastrointestinal infections

  • Colon cancer

  • STIs

  • Tuberculosis

  • Other forms of colitis

  • Toxic megacolon

Blood tests for P-ANCA and ASCA can aid in differentiating ulcerative colitis from Crohn’s. A high fecal calprotectin level confirms inflammation in the GI tract but cannot specify whether it’s ulcerative colitis or Crohn's.

Screening for Comorbid Conditions

Ulcerative colitis may occur alongside other health problems. Providers may screen for:

  • Arthritis

  • Cardiovascular disease

  • Liver and kidney disorders

  • Respiratory conditions

  • Migraines or chronic headaches

  • Certain cancers

A Quick Review

Ulcerative colitis is a chronic inflammatory condition affecting the colon and rectum. Diagnosis involves collecting a detailed medical history, conducting physical and lab exams, and confirming the condition through endoscopy and biopsy.

Once diagnosed, providers classify the disease based on severity and how far it has spread. They also screen for related conditions and comorbidities to ensure comprehensive care. Early detection and proper staging are essential for effective treatment and long-term management.