Assessing diarrhoea

If you have diarrhoea your doctor or nurse will ask you some questions and they might do some tests. This is to assess how severe your diarrhoea is, the cause of your diarrhoea, and whether you need treatment.

Effects of diarrhoea on the body

Diarrhoea can affect your body in different ways:


Diarrhoea can cause dehydration Open a glossary item. When you have diarrhoea, food passes quickly through the bowel before your body absorbs the vitamins, minerals and water. And fluid is also drawn out of the cells in your body into the bowel. The fluid is released in your poo (stool or faeces). 

Losing large amounts of fluid can be dangerous for your body. And you can feel very weak and tired.

Loss of sodium, potassium, and calcium (electrolytes)

Along with fluid, you also lose important chemicals from the cells of your body. These chemicals are called electrolytes. They include sodium, potassium, calcium magnesium, and phosphate, 

The electrolytes must be in a certain balance for the body to work normally. When the electrolytes get out of balance it can be harmful to your kidneys and other organs in your body.

Sore skin around the back passage (anus)

The salts in the diarrhoea can also make the skin around your anus very sore after a while.

Grading the diarrhoea

Health professionals use a grading system for diarrhoea from 1 to 4. Grade 1 is mild diarrhoea and grade 4 is the most severe. Your doctor or nurse will want to know how severe it is and what is causing it. They can then plan the best treatment for you.


Your doctor will examine you and possibly arrange some tests and investigations, these may include:

  • blood tests
  • sending a sample of poo to the laboratory to find out if you have an infection

You might have a CT or ultrasound scan if your specialist needs more information. They will tell you more about these tests and explain why you need them.  

Questions your doctor or nurse might ask

  • How long have you had diarrhoea?
  • How many times a day and night are you opening your bowels?
  • Are you taking any medicines?
  • What does your poo look like?
  • Does it happen at particular times such as after you have eaten or after your cancer treatment?
  • Are you taking any medicines to help?
  • How much is your diarrhoea stopping you from doing day to day things?

Your doctor will give you advice about ways to help yourself and might prescribe medicines to control the diarrhoea.

Talking about your diarrhoea

You might find it hard to talk about having diarrhoea. You may feel embarrassed or upset, or worried about what the diarrhoea means. These feelings are very natural.

Remember that your doctors and nurses will be aware of your worries and are used to talking about them. They can reassure you and suggest ways of managing your diarrhoea.

Some people say that diarrhoea is one of the hardest aspects of cancer treatment to cope with. So it is very important that you get some help.

If you find it difficult to talk to your doctors or nurses, it might help to write down the problems you have. You can give the list to your doctor or nurse to read. It can also help to have a friend or relative go with you and do the talking.

If you have treatment in an open day unit, you can ask to go into a private room to discuss your diarrhoea. Your doctors and nurses are aware that you might want to talk in private sometimes, so don’t be afraid to ask.

Although you might find it embarrassing to speak to your doctor or nurse about your diarrhea, remember they are used to talking about this and will want to help. And the sooner they can treat it the more comfortable you will feel.

  • Assessment and management of diarrhoea in adults
    National Institute for Health and Care Excellence (NICE), revised May 2021

  • Diarrhoea in adult cancer patients: ESMO Clinical Practice Guidelines

    P. Bossi and others

    Annals of Oncology. 2018, Volume 29, Supplement 4

  • Guidelines for the investigation of chronic diarrhoea in adults: British Society of Gastroenterology, 3rd edition

    R P Arasaradnam and others

    Gut, 2018. Volume 67, Issue 8, Pages 1380–1399.

Last reviewed: 
09 Dec 2022
Next review due: 
09 Dec 2025

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