Severe Diarrhoea — The Emergency Most Families Miss

Seven or more loose stools a day above your usual baseline — or any stools with blood, mucus, fever, dizziness or reduced urination — is the threshold oncology teams treat as an emergency on immunotherapy. This is not the same as ordinary stomach upset: it can be immune-related colitis, and the count alone is enough reason to call the same day, even without any of the other signs.

Blood or mucus in the stool, fever, severe cramping, dizziness, a fast heartbeat, and reduced or dark urination alongside diarrhoea all point to something beyond ordinary stomach upset. Any one of these — even with a lower stool count than the threshold above — is treated as a same-day or emergency-room situation, because it suggests bowel inflammation or dehydration has already progressed.

• Blood or mucus in the stool — never a normal finding, whatever the suspected cause.
• Fever with abdominal pain — can signal the inflammation is more advanced.
• Dizziness, fainting or a fast heartbeat — early signs of dehydration losing ground.
• Little or no urination — a practical, at-home marker of dehydration you can check without any equipment.
• Confusion or unusual drowsiness — needs emergency assessment, not a phone call alone.

Do not take over-the-counter anti-diarrhoeal tablets, try herbal or home remedies, or "wait a day to see" once symptoms reach the levels above. These responses are built for infectious or dietary diarrhoea, not immune colitis, and they can mask exactly how fast the reaction is progressing — the one thing you cannot afford to lose sight of in an emergency.

• Don't self-medicate — anti-diarrhoeal or anti-nausea tablets taken without your oncology team's knowledge can hide worsening symptoms.
• Don't wait for your next scheduled appointment — immune colitis can escalate from mild to severe within days, sometimes hours.
• Don't assume it's food poisoning and "ride it out" — the two can look identical, and only one of them gets worse without steroid treatment.
• Don't drive yourself if you're dizzy or very weak — call for help or have someone take you; say clearly that you are on cancer immunotherapy.

There is no safe home-management step for the emergency signs described above. The only correct action is to call the CION helpline now, or go straight to the nearest emergency room if you have severe dehydration signs, fainting or confusion.

Calling early leads to a structured emergency pathway, not guesswork — your symptoms are graded, infection is ruled out, and treatment starts promptly if immune colitis is confirmed. See our companion page, Immune Colitis: What It Is and How It Is Treated, for the full clinical picture.

1. 1

   Same-day or emergency triage call

   You describe your stool count and any other symptoms; the team decides whether to bring you in immediately or the same day.

2. 2

   Severity grading

   Your clinician grades the reaction — mild, moderate or severe — using standard oncology criteria, based on frequency and associated symptoms.

3. 3

   Ruling out infection

   Stool tests are usually sent first, since a bacterial or viral cause needs different treatment from immune colitis.

4. 4

   Steroids and a treatment pause

   If immune colitis is confirmed, steroids are typically started promptly and immunotherapy is paused while you're monitored closely.

Severe diarrhoea is one of several immune reactions that can be fatal if treated as ordinary illness. These companion pages cover the others worth recognising.

• Sudden Breathlessness on Immunotherapy — when new shortness of breath needs emergency assessment, not a wait-and-see approach.
• Chest Pain on Immunotherapy: Never Wait — why chest pain or palpitations on immunotherapy always mean going now.
• Severe Weakness, Collapse or Confusion — the neurological and endocrine emergencies families most often miss.
• Immunotherapy at CION Cancer Clinics — how we monitor and support patients through immune-related side effects, from the first infusion onward.

Immune Emergencies Are Manageable When Caught Early

Patients who call at the first red-flag sign are supported by the same multidisciplinary team throughout treatment.