The hallmark sign of diverticulitis is abdominal pain, most often on the lower left side, that comes on suddenly and feels severe. If you’re also running a fever and noticing changes in your bowel habits, those three symptoms together are the strongest signal that a pouch in your colon wall has become inflamed or infected. You can’t confirm diverticulitis at home, but knowing what to look for helps you decide how quickly to seek care.
The Main Symptoms
Diverticulitis pain typically settles in the lower left abdomen because that’s where the colon pouches (called diverticula) most commonly form. The pain is usually severe and starts abruptly, though in some cases it begins mild and worsens over several days. It often gets worse when you press on the area, and your belly may feel swollen or hard to the touch.
Beyond the pain, other common symptoms include:
- Fever and chills
- Nausea or vomiting
- Constipation (more common) or sudden diarrhea
- Rectal bleeding
- A visibly distended abdomen
Not everyone gets all of these. Some people have only pain and a low-grade fever. Others have significant digestive disruption with nausea and constipation but relatively mild pain. The combination matters more than any single symptom.
How It Differs From Diverticulosis
Most people who develop diverticulitis already have diverticulosis, a condition where small pouches have formed in the colon wall. Diverticulosis is extremely common and usually causes no symptoms at all. Many people discover they have it only when a doctor images their abdomen for an unrelated reason.
Some people with diverticulosis notice mild, chronic symptoms like bloating, cramping, or irregular bowel habits. The key difference is intensity: diverticulosis symptoms are low-grade and ongoing, while diverticulitis pain is acute, often severe, and paired with fever or other signs of inflammation. If you’ve had mild belly discomfort for weeks, that’s less likely to be diverticulitis than if you woke up this morning with sharp lower-left pain and a temperature of 101°F.
Conditions That Look Similar
Several other problems can cause lower abdominal pain and mimic diverticulitis closely. Irritable bowel syndrome produces cramping and bowel changes in the same region, though it rarely causes fever. Inflammatory bowel disease (Crohn’s or ulcerative colitis) can produce pain, fever, and diarrhea that overlap heavily with diverticulitis symptoms. Colon cancer can even look nearly identical on imaging.
For women, the overlap is wider. Ovarian cysts, ectopic pregnancy, endometriosis, and pelvic inflammatory disease can all produce lower abdominal pain with nausea. A urinary tract infection or kidney stone can also land in the same general area. This is one reason doctors rely on imaging rather than symptoms alone to make the diagnosis.
It’s Not Just an Older Person’s Problem
Diverticulitis has traditionally been seen as a condition affecting people over 50, but that’s shifting. A UCLA and Vanderbilt analysis of 5.2 million U.S. hospital admissions for diverticulitis between 2005 and 2020 found that about 16% of cases occurred in patients younger than 50. More concerning, the share of younger patients with complicated diverticulitis (involving abscesses, perforations, or other serious problems) rose from 18.5% to 28.2% over that period. If you’re in your 30s or 40s and experiencing these symptoms, your age alone doesn’t rule it out.
What Happens at the Doctor’s Office
A doctor evaluating you for possible diverticulitis will start with a physical exam: checking your temperature, pressing on your abdomen to find areas of tenderness or masses, listening to your gut sounds with a stethoscope, and possibly performing a digital rectal exam. They’ll ask about when the pain started, where exactly it hurts, and whether you’ve had fever or bowel changes.
Blood tests come next. Your doctor will look at your white blood cell count and a marker called C-reactive protein (CRP), both of which rise with inflammation and infection. It’s worth noting that white blood cell counts come back normal in nearly half of diverticulitis cases, so a normal result doesn’t rule it out. CRP tends to be a more sensitive indicator. If your doctor suspects perforation or a more complicated case, very high CRP levels (above 200 mg/L) raise that concern. A urinalysis and pregnancy test may also be ordered to rule out other causes.
Why a CT Scan Is Usually Needed
A CT scan of the abdomen and pelvis with contrast dye is the standard diagnostic tool. It can confirm inflamed diverticula, show how severe the episode is, reveal complications like abscesses or perforations, and help distinguish diverticulitis from conditions that look similar. Major medical guidelines recommend it as the first imaging step for suspected cases, and it has a sensitivity around 94% and specificity around 99%, meaning it catches nearly all true cases and rarely returns a false positive.
You typically won’t need a colonoscopy during an acute flare. In fact, it’s usually avoided because the colon is inflamed and more vulnerable to injury. Your doctor may recommend a colonoscopy weeks after you’ve recovered, particularly if it’s your first episode, to rule out colon cancer or other structural problems that can look like diverticulitis on a CT scan.
Symptoms That Need Urgent Attention
Most diverticulitis episodes are uncomplicated, meaning the inflammation responds to rest and antibiotics without surgery. But some cases involve serious complications that need emergency care. Seek immediate medical attention if you experience severe, worsening abdominal pain that doesn’t ease with position changes, a high fever (above 102°F), significant rectal bleeding, persistent vomiting that prevents you from keeping fluids down, or an abdomen that becomes rigid and extremely tender to any touch. These can signal a perforation (a hole in the colon wall), an abscess, or a blockage, all of which may require hospital admission or surgery.
Constant, unexplained abdominal pain paired with fever and notable stool changes warrants medical evaluation even if the symptoms don’t feel like an emergency. Diverticulitis that goes untreated can progress from a simple inflammation to a complicated one, and early treatment makes a significant difference in outcomes.