CCFP priority topic 27 of 105
Diarrhea on the CCFP exam
7 key features, the mistakes that cost marks, and a practice question.
Checked by a Canadian family physician, MD, CCFP. Updated October 22, 2026.
What the exam tests
Key features
The CFPC’s 7 key features for Diarrhea. Each one below has how the exam asks it, the common mistakes and the approach.
Practice question
Try one before you read
A real case from the bank, in the new short-menu format. Answer it first. Then read the key features.
Key feature 1 of 7
Fluid loss first
Judge how dry a patient with diarrhea is, then replace the loss.
CFPC skill Clinical reasoningPhase Diagnosis, treatment
On the exam
A feverish, vomiting 9-month-old with watery stools. Expect a short menu (pick several from a list) of signs, then one best answer.
Pick the signs that grade the loss, then the fluid.
Common mistakes
Sizing the loss with blood tests or an X-ray. Or trusting a sunken fontanelle, or a fast pulse in a crying, feverish baby.
Approach
- Grade the loss as none, mild to moderate, or severe. Use how the child looks, the eyes, the mouth, tears, skin and breathing.
- In an adult or older adult, judge the loss from lying and standing pulse and blood pressure, and from new confusion.
- A recent known weight is the best yardstick. Compare it with today's weight.
- A sunken fontanelle, a fast pulse with fever, and wet-diaper counts with watery stools all mislead. Do not let them set the plan.
- No loss: usual feeds and fluids. Keep breastfeeding.
- Mild to moderate loss: rehydrate by mouth in small, frequent sips.
- Still vomiting: give smaller, more frequent sips. A tube through the nose to the stomach (nasogastric), then IV, only if that fails. Restart usual feeds once rehydrated.
| Signs | Treat with | |
|---|---|---|
| None | Alert, moist mouth, tears present | Usual feeds and fluids; keep breastfeeding |
| Mild to moderate | Fussy, dry mouth, sunken eyes, slow skin recoil or colour return | Rehydrate by mouth in small, frequent sips |
| Severe | Drowsy or limp, cold hands and feet, too weak to drink | IV fluid now |
Key feature 2 of 7
Cause from the story
In new-onset diarrhea, let the history point you to the likely cause.
CFPC skill Clinical reasoningPhase Hypothesis generation, historySources Choosing Wisely Canada, Public Health Agency of Canada (CATMAT) 2015
On the exam
Two days of fever, vomiting and watery stools, with sick children in the same daycare room. Expect a short menu (pick several from a list) of questions.
Pick the questions that point to the cause.
Common mistakes
Chasing cow's milk allergy, giardia or intussusception when fever, vomiting and sick contacts point to infection. Or sending a stool culture that will not change today's plan.
Approach
- Ask who else is sick: at home, daycare, school, on a ward or in a care home.
- Ask about a shared meal. Several ill people who ate at one place point to food poisoning.
- Ask about travel, camping, untreated water and contact with animals. After travel, in more severe illness, send a stool culture to find the germ and the antibiotics that work.
- Ask about every drug started lately: antibiotics, metformin, magnesium, laxatives, new supplements.
- A hospital stay or an antibiotic in recent weeks points to C. difficile (key feature 3).
- Match the pattern. Fever and vomiting with sick contacts fit a virus. Weeks of greasy, foul stools and bloating fit giardia. Bouts of pain and later bloody stool fit intussusception (bowel telescoping into itself).
- Under 1 year, C. difficile is rarely the cause, even after antibiotics. Many infants carry it without being ill.
Key feature 3 of 7
C. difficile
After a hospital stay or an antibiotic, think of C. difficile as the cause.
CFPC skill Clinical reasoningPhase Hypothesis generationSources Choosing Wisely Canada
On the exam
Watery stools days after discharge, in a child fed by gastrostomy. Expect one best answer for the stool test.
Pick the test that finds the cause.
Common mistakes
A routine stool culture, a parasite test or a viral panel: none looks for C. difficile. Routinely testing an infant, or testing formed stool or a cured patient, is wrong too.
Approach
- Think of C. difficile in new watery diarrhea after an antibiotic, or after a hospital or care-home stay.
- Test liquid stool only. A positive result without diarrhea likely means the germ is just carried, not causing disease.
- Do not repeat a nucleic acid (PCR) test within 7 days of a negative one. It adds little.
- Do not test infants under 1 year routinely. Many carry it without illness, and disease is rarely seen before 12 to 24 months.
- From 1 to 3 years, look for other causes first, mostly viruses.
- No test of cure after treatment.
| Situation | Test? | Why |
|---|---|---|
| Watery stools after antibiotics or a hospital stay | Yes, on liquid stool | The story fits |
| Formed stool | No | A positive result likely means carriage |
| Infant under 1 year | Not routinely | Many carry it without illness |
| Negative PCR in the past 7 days | No | A repeat adds little |
| Well after treatment | No | Test of cure is not recommended |
Key feature 4 of 7
Back to school or work
Tell the patient when it is safe to go back to work, school or daycare.
CFPC skill Clinical reasoningPhase TreatmentSources Choosing Wisely Canada
On the exam
A child treated for C. difficile, with formed stools for two days. Expect one best answer on return to school.
Pick when the patient can go back.
Common mistakes
Sending the child back while stools are still loose. Or keeping the child home until the antibiotic course ends. A parent's lost shifts do not shorten it.
Approach
- Tie the return to the diarrhea settling, not to the last pill.
- In an adult after C. difficile, no test of cure before going back to work. The return follows the diarrhea.
- Keep the patient home while stools are still loose, and with fever, vomiting or blood in the stool.
- In a declared outbreak, public health sets a longer symptom-free wait. Follow it.
- Food handlers, health care workers and child care staff may face stricter rules, which can include stool tests. Check with local public health.
- Teach hand washing with soap and water. Alcohol gel does not kill C. difficile spores.
Key feature 5 of 7
Older adults
Investigate new diarrhea with no clear cause in an older adult, and do not wait.
CFPC skill Clinical reasoning, selectivityPhase Hypothesis generation, investigationSources Canadian Association of Gastroenterology, Choosing Wisely Canada
On the exam
A 74-year-old with six weeks of new loose stools and a normal screening stool test last year. Expect a short menu (pick several from a list) of next steps.
Pick the work-up, and how soon.
Common mistakes
Calling it irritable bowel syndrome (IBS) or a lingering virus and waiting. Or leaning on last year's normal screening stool test.
Approach
- New IBS-type symptoms at 50 or older: refer for colonoscopy to rule out other causes.
- Do not work up symptoms with a stool blood test, guaiac or fecal immunochemical test (FIT). FIT is for screening people without symptoms.
- Watery diarrhea in a woman over 45: think of microscopic colitis, an inflammation seen only on biopsy. Ask for biopsies at colonoscopy.
- Review every drug: new ones, laxatives, metformin, magnesium and recent antibiotics.
- In long-term care, check for hard stool in the rectum. Liquid stool can leak around it.
- A mass, dark red rectal bleeding or marked weight loss need prompt investigation at any age.
Key feature 6 of 7
IBS in the young
In a young patient with long-standing loose stools and no alarm features, diagnose IBS from symptoms.
CFPC skill Clinical reasoning, selectivityPhase DiagnosisSources Canadian Association of Gastroenterology, Choosing Wisely Canada
On the exam
A 24-year-old with cramps and loose stools for a year, worse with stress, no alarm features. Expect a short menu (pick several from a list) of tests.
Pick the tests worth sending, and skip the rest.
Common mistakes
A colonoscopy to reassure, or C-reactive protein (CRP), fecal calprotectin, allergy tests or routine breath tests. A normal scope does not reassure patients more than no scope. Skipping celiac serology is the opposite error.
Approach
- Use the Rome IV criteria. Belly pain at least 1 day a week for 3 months, tied to bowel movements or a change in stools.
- Subtype by stool form. IBS with diarrhea: more than a quarter of stools loose, fewer than a quarter hard.
- Send a celiac blood test (serology) once. If it is negative, no gluten-free diet is needed for celiac disease.
- No routine CRP or fecal calprotectin (a stool marker of gut inflammation). Save them for a high suspicion of inflammatory bowel disease.
- Under 50 with no alarm features: no routine colonoscopy.
- No food allergy testing, and no routine lactose or glucose breath tests.
- Alarm features such as rectal bleeding, weight loss or anemia change the plan. Work them up (key feature 7).
| Test | Use it? | Why |
|---|---|---|
| Celiac serology | Yes, once | Celiac symptoms overlap with IBS |
| CRP, fecal calprotectin | Not routinely | Only if inflammatory bowel disease is strongly suspected |
| Colonoscopy under 50, no alarm features | No | Low yield; it does not reassure patients more |
| Colonoscopy, new symptoms at 50 or older | Yes | Rules out other causes |
| Food allergy or breath tests | No; breath tests not routinely | Recommended against in IBS |
Key feature 7 of 7
Clues to a disease
When diarrhea lasts or keeps coming back, seek gut and whole-body clues to an underlying disease.
CFPC skill Clinical reasoningPhase History, physicalSources Canadian Association of Gastroenterology, Choosing Wisely Canada
On the exam
Months of loose stools with weight loss, mouth ulcers and sore joints. Expect a short menu (pick several from a list) of findings to look for.
Pick the findings that point to a cause.
Common mistakes
Stopping at the bowel history and calling it IBS. Or missing the clues outside the gut, such as mouth ulcers, sore joints or a tremor.
Approach
- Alarm features raise the chance of another disease: bleeding, weight loss, anemia, vomiting, a mass, trouble swallowing. Work them up before you call it IBS.
- Inflammatory bowel disease: blood or mucus, stools at night, fever, weight loss. Outside the gut: mouth ulcers, joint pain, red eyes, skin sores, sores around the anus.
- Malabsorption: pale, greasy, floating stools, weight loss, low iron, and poor growth in children.
- Celiac disease: an itchy, blistering rash, iron deficiency, poor growth. Send celiac serology when diarrhea leads the picture.
- Weak immunity: HIV risk, repeated infections, thrush, chemotherapy or transplant drugs.
- Causes outside the gut: an overactive thyroid (tremor, heat intolerance, weight loss) and diabetes.
Flashcards
Answer it first, then check.
KF 1An alert 9-month-old is moderately dry and still vomiting. What first?
Rehydrate by mouth in small, frequent sips. A tube through the nose to the stomach (nasogastric), then IV, only if that fails.
KF 3Watery stools began two weeks after a hospital stay. Which stool test?
A C. difficile test on liquid stool. A routine culture does not look for it. Source: Choosing Wisely Canada
KF 3A 9-month-old on amoxicillin has loose stools. Test for C. difficile?
Not routinely. Many infants under 1 year carry it without illness. Look for other causes. Source: Choosing Wisely Canada
KF 4An adult treated for C. difficile has had formed stools for two days. Retest before work?
No. Test of cure is not recommended. A positive result without diarrhea likely means carriage. Source: Choosing Wisely Canada
KF 5New loose stools at 72, and a normal screening stool test last year. Next step?
Colonoscopy. New bowel symptoms at 50 or older need it, whatever last year's screening showed. Source: Canadian Association of Gastroenterology
KF 6A 24-year-old fits Rome IV for IBS with diarrhea, no alarm features. Which test?
Celiac serology, once. Skip colonoscopy, CRP and fecal calprotectin. Source: Canadian Association of Gastroenterology
KF 7Months of diarrhea with mouth ulcers and a red, sore eye. What do you suspect?
Inflammatory bowel disease. Ask about blood, stools at night, weight loss and joint pain.
FAQ
Is it Clostridium or Clostridioides difficile?
The same germ. It was renamed Clostridioides difficile a few years ago, but many labs and older papers still say Clostridium. C. difficile covers both, and the exam may use either.
Do I need to recite the Rome IV criteria word for word?
No. Know the core: belly pain at least weekly for 3 months, tied to bowel movements or stool change. Marks go to diagnosing IBS from symptoms, without piling on tests.
Why not try a gluten-free diet instead of testing for celiac disease?
Test first, while the patient still eats gluten. A diet started first can hide the diagnosis. Test once. If it is negative, no gluten-free diet is needed for celiac disease.
Sources
Written from the CFPC Assessment Objectives and Canadian guidelines first. Checked by a Canadian family physician, MD, CCFP.
Last reviewed October 22, 2026For exam study. Not advice for a patient in front of you.
- Assessment Objectives for Certification in Family Medicine, 2nd editionCollege of Family Physicians of Canada · 2020
- Choosing Wisely recommendationsChoosing Wisely Canada
- Statement on Travellers' DiarrheaPublic Health Agency of Canada (CATMAT) · 2015
- Gastroenterology guideline libraryCanadian Association of Gastroenterology