IBS red flags: symptoms that need a doctor, not a diary

What a red flag means

A red flag is a symptom or sign that makes a doctor look for something other than IBS. The UK’s NICE guideline on IBS in adults says that everyone with possible IBS symptoms should be assessed for red flag indicators, including signs and symptoms of cancer and inflammatory markers for inflammatory bowel disease, and referred for further investigation if any are present.

IBS itself is a long-term condition of pain and bowel changes. NIDDK says doctors diagnose it from a pattern of symptoms, and that certain symptoms may suggest another health problem instead. Having one red flag does not mean you have a serious disease. It means a doctor should check.

Symptoms to take to a doctor

NIDDK and the NHS name the same core warning signs. Take any of these to a doctor, and do not explain them away with food.

• Bleeding from the rectum, or bloody diarrhea (NIDDK, NHS).
• Stools that are black and tarry (NIDDK).
• Weight loss you cannot explain (NIDDK, NHS).
• Anemia, found on a blood test (NIDDK). The NHS lists shortness of breath, noticeable heartbeats and skin paler than usual as signs that could be something more serious.
• A hard lump or swelling in your belly (NHS).
• Pain that stays in one fixed place. NICE notes that IBS pain can be anywhere in the abdomen and may vary, which distinguishes it from cancer-related pain, which typically has a fixed site.

Age, family history and new symptoms

The American College of Gastroenterology’s patient page lists warning signs a doctor checks for: rectal bleeding, unexplained weight loss, low iron levels, new symptoms later in life and a family history of colon cancer. If they are present, a test such as a colonoscopy may be needed. NIDDK adds a family history of celiac disease or inflammatory bowel disease to what the doctor will ask.

NICE’s guideline on suspected cancer gives age thresholds for the United Kingdom, which are not US rules but show how age changes the picture. Adults with an abdominal mass, a change in bowel habit or iron-deficiency anemia are offered a stool test for blood. So are adults aged 40 and over with unexplained weight loss and abdominal pain, those aged 50 and over with unexplained rectal bleeding, abdominal pain or weight loss, and those aged 60 and over with anemia.

For women, NICE says to test for ovarian cancer in a woman aged 50 or over who has had symptoms in the past 12 months that suggest IBS, because IBS rarely presents for the first time at this age. It also lists persistent abdominal bloating, particularly more than 12 times a month, as a symptom that calls for tests in women.

How fast to act

The NHS says to see a doctor if you think you have IBS and have had symptoms for more than 4 weeks, so that they can check and rule out other problems. For the more serious signs, it says to ask for an urgent appointment, or get help from NHS 111 (the UK health line), if you have lost a lot of weight for no reason, are bleeding from your bottom or have bloody diarrhea, find a hard lump or swelling in your belly, or have shortness of breath, palpitations and unusually pale skin.

Practical advice from us, not from those sources: in the United States, call your doctor the same day for bleeding, black stools or a lump, and call 911 or go to emergency care if you feel faint, have severe belly pain that does not ease, or pass a lot of blood or black stool.

What the doctor will do

NIDDK says that most of the time doctors do not use tests to diagnose IBS, but may order blood tests and stool tests to check for anemia, infection and digestive diseases, and may recommend a colonoscopy to look for conditions such as colon cancer or inflammatory bowel disease. The ACG guideline suggests blood tests for celiac disease in people with IBS and diarrhea, and a stool test called fecal calprotectin to rule out inflammatory bowel disease.

The ACG guideline also favors a positive diagnostic strategy, which means diagnosing IBS from its symptom pattern instead of testing for everything else first. That works when no red flags are present. When they are, expect tests.

What to do before the appointment

Practical advice from us: write down when each symptom started, how often it happens, what the stool looks like, any blood or black stool, your weight if you track it, and what runs in your family. Bring a list of medicines and supplements.

Hold off on a restrictive diet until the doctor has seen you. The ACG guideline recommends a limited low-FODMAP trial for people with IBS, so it belongs after the diagnosis, not before.