CCFP priority topic 84 of 105
Renal Failure on the CCFP exam
10 key features, the mistakes that cost marks, and a practice question.
Checked by a Canadian family physician, MD, CCFP. Updated October 20, 2026.
What the exam tests
Key features
The CFPC’s 10 key features for Renal Failure. 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 10
Name the diagnosis
Tell a patient with chronic kidney disease they have it, and what it means for them.
CFPC skill Communication, patient-centred approachPhase TreatmentSources Canadian Association of Radiologists 2022, Choosing Wisely Canada
On the exam
A low estimated glomerular filtration rate (eGFR) for two years that nobody has named. Expect one best answer.
Pick what to tell the patient first.
Common mistakes
Saying nothing because the patient feels well, or calling it a little kidney weakness. Unnamed disease means painkillers, dehydration and drug doses go unwatched.
Approach
- Name it: chronic kidney disease. Give the stage and say what the numbers mean.
- Explain why it matters: kidney function guides drug doses, scans with contrast dye, and what to do on sick days.
- Tell the patient to say "I have kidney disease" at every pharmacy and scan booking. Radiology clinics ask exactly that.
- Name the painkillers to avoid: anti-inflammatory painkillers (NSAIDs) such as ibuprofen and naproxen.
- Ask what the patient understood. Plan the next blood and urine tests together.
Key feature 2 of 10
Contrast and metformin
Prevent kidney injury when a test and a drug together could harm the kidneys.
CFPC skill Clinical reasoningPhase Hypothesis generation, treatmentSources Canadian Association of Radiologists 2022
On the exam
A man on metformin needs a contrast CT scan after a vomiting illness. Expect a short menu (pick several from a list).
Pick the steps before and after the scan.
Common mistakes
Ordering N-acetylcysteine or half-dose contrast by habit; neither protects the kidneys. Preventive fluids add nothing above an eGFR of 30. Or waving through an eGFR of 22 with acute injury without a deliberate decision.
Approach
- Inpatients and emergency patients: use an eGFR from the last 7 days.
- Stable outpatients with no eGFR on file: ask whether they have kidney problems or see a kidney specialist. Check an eGFR (within 3 to 6 months) only if the answer is yes.
- Emergency scan: do not wait for the eGFR. Do not withhold contrast the diagnosis needs.
- eGFR above 30 and no acute injury: go ahead. Keep metformin. No fluids before and no creatinine check after.
- eGFR 30 or less, or acute injury: weigh kidney risk against a late or missed diagnosis, with the patient. Hold metformin at or before the scan.
- Restart metformin after at least 48 hours, and only if creatinine stays within 25% of baseline and the team has reviewed it.
- Skip N-acetylcysteine and statins for kidney protection. Do not cut the CT contrast dose: it weakens the images.
- A bowel preparation can drain fluid too. Ask about kidney disease first, and plan fluids around it.
| eGFR above 30, no acute injury | eGFR 30 or less, or acute injury | |
|---|---|---|
| The scan | Go ahead with an indicated scan | Decide with the patient: injury risk against a missed diagnosis |
| Metformin | Keep it | Hold at or before the scan. Restart after 48 hours or more, if creatinine is stable and reviewed. |
| Fluids before | Not recommended | No recommendation for contrast into a vein; local practice |
| ACE inhibitor, ARB, diuretic | Do not stop routinely | Do not stop routinely |
| Creatinine after | Not needed | At 48 to 72 hours, after contrast into an artery |
Key feature 3 of 10
Prescribing safely
Before prescribing in kidney disease, check safety and dose, then watch kidney function more closely.
CFPC skill Clinical reasoning, selectivityPhase Treatment, follow-upSources Choosing Wisely Canada
On the exam
A man with an eGFR of 34 starts several drugs in hospital for an abscess. Expect a short menu (pick several from a list).
Pick the drugs that threaten the kidneys.
Common mistakes
Flagging every drug on the chart. Low molecular weight heparin and many antibiotics need a dose or interval change, not removal. The real threat is a drug that injures kidneys.
Approach
- Look up each drug at the patient's eGFR. Some need a lower dose, some a longer interval, some avoiding.
- Many drugs need a lower dose or longer interval, including some antibiotics and blood thinners.
- Do not pair an angiotensin-converting enzyme (ACE) inhibitor with an angiotensin receptor blocker (ARB). Together they bring low blood pressure, acute kidney injury and high potassium.
- In kidney disease or on dialysis, review the whole drug list and pill burden at every renewal.
- On dialysis, weigh bleeding risk before warfarin or a direct oral anticoagulant for atrial fibrillation.
- For chronic pain, try non-drug and non-opioid options before opioids.
- After starting or changing a drug that affects the kidneys, recheck creatinine and potassium sooner than usual.
Key feature 4 of 10
Fluids
Teach patients with advanced kidney disease to keep up fluids when heat, travel or illness drains them.
CFPC skill Clinical reasoningPhase Treatment
On the exam
An older woman with advanced kidney disease plans a summer trip. Expect a short menu (pick several from a list).
Pick the advice to give her.
Common mistakes
Telling every kidney patient to limit fluids. Limits are for fluid overload or dialysis. For most patients, drying out is the bigger threat.
Approach
- Name the risky times: hot weather, long travel, hard exercise, vomiting, diarrhea and fever.
- Older adults feel thirst less. In a heat wave, drink by the clock, not by thirst.
- Warn that water pills add to fluid loss on hot days.
- Fluid limits are for people who are overloaded or on dialysis. Do not start one without a reason.
- Teach the signs of drying out: dizziness on standing, dark urine, much less urine.
- Link it to the sick-day plan. When fluids cannot keep up, some drugs pause.
Key feature 5 of 10
Pharmacy products
Steer patients with kidney disease away from store-bought products that can harm the kidneys.
CFPC skill Clinical reasoningPhase TreatmentSources Choosing Wisely Canada
On the exam
A parent lists the pharmacy products a child with kidney disease takes. Expect a short menu (pick several from a list).
Pick the products that threaten the kidneys.
Common mistakes
Flagging everything. Acetaminophen at usual doses, a probiotic or one cranberry capsule does not harm kidney function. Missing the NSAID is the costly error.
Approach
- Tell every patient with kidney disease to avoid NSAIDs: ibuprofen, naproxen and celecoxib alike.
- Explain why: NSAIDs raise blood pressure, blunt blood pressure drugs, hold fluid and can lower kidney function.
- Check cold remedies and combination painkillers for a hidden NSAID.
- Ask about herbals and supplements at every visit. Patients often do not call them medicines.
- Offer a pain plan without NSAIDs, and ask the pharmacist to flag them too.
Key feature 6 of 10
Sick-day rules
Give patients with advanced kidney disease a plan for illnesses that stop them drinking.
CFPC skill Clinical reasoning, selectivityPhase Treatment
On the exam
A child on enalapril has vomited every sip for a day. Expect one best answer.
Pick the advice for the family.
Common mistakes
Holding the drug but arranging no visit, or halving the dose instead. Holding it for every fever is wrong too, if the child drinks well.
Approach
- Give the plan before illness strikes, in writing.
- The trigger: vomiting, diarrhea or fever, with too little fluid kept down.
- Pause ACE inhibitors, ARBs, water pills and any NSAID.
- Hold, do not halve.
- Get seen soon for creatinine and potassium. A patient who cannot drink needs an exam, not only a paused pill.
- Restart once eating and drinking normally. A fever with normal drinking is not a reason to stop.
Key feature 7 of 10
Acute on chronic
When kidney function falls further, fix the cause, pause harmful drugs, and plan when to resume them.
CFPC skill Clinical reasoning, selectivityPhase TreatmentSources Canadian Association of Radiologists 2022
On the exam
Rising creatinine and little urine after fluids, in a man with an enlarged prostate. Expect one best answer.
Pick the next step.
Common mistakes
More fluid or a diuretic for scant urine. With a full bladder on scan, urine cannot get out. Drain it before anything else.
Approach
- Acute injury: creatinine up more than 26 µmol/L in 48 hours, or more than 50% in 7 days.
- Or urine under 0.5 mL/kg/hour for 6 to 12 hours.
- Look for the cause: fluid loss, infection such as pneumonia, heart failure, a blocked bladder.
- Scan the bladder early. If it is full, put in a catheter now. Image later only if function does not recover.
- Pause drugs that cut kidney blood flow or build up in kidney failure while function is falling.
- Do not trust the eGFR while creatinine is changing. Follow the creatinine itself.
- Restart the ACE inhibitor once creatinine is back near baseline and the patient is drinking.
- After a restart, recheck creatinine and potassium soon. Raise the dose only after that check.
Key feature 8 of 10
Regular follow-up
Recheck kidney function on a schedule, because kidney disease can quietly progress.
CFPC skill Clinical reasoningPhase Follow-upSources Canadian Association of Radiologists 2022
On the exam
A stable patient with chronic kidney disease returns for a review. Expect a short menu (pick several from a list).
Pick the tests to order.
Common mistakes
Ordering staging tests during an acute illness, when the results mislead. Or calling one low value chronic without a repeat.
Approach
- Chronic means changes that last more than 3 months. Repeat a new low result before you call it chronic.
- Test when the patient is well, not during an acute illness.
- Plot results over time. One low value may be noise; a steady fall is not.
- At each review, check blood pressure, potassium and the drug list.
Key feature 9 of 10
When to refer
Decide when a patient with kidney disease needs a specialist, given the patient and local services.
CFPC skill Clinical reasoning, selectivityPhase Treatment, follow-upSources Choosing Wisely Canada
On the exam
A 32-year-old with a mildly low eGFR and protein in the urine. Expect a short menu (pick several from a list).
Pick who needs a nephrologist.
Common mistakes
Watching mild disease in a young adult because the number looks safe. Or referring a frail older patient with stable disease who would not gain from it.
Approach
- Refer when function falls fast, eGFR is very low, or the urine holds a lot of protein.
- Refer mild disease in a young adult. Decades lie ahead, and the cause matters.
- Refer blood and protein together in the urine, or blood pressure that resists several drugs.
- Refer bone and mineral problems: abnormal calcium, phosphate or parathyroid hormone.
- Refer anemia that persists once iron is replaced. Red-cell boosting drugs are not started at hemoglobin 100 g/L or more without symptoms.
- Use an electronic consult or phone advice where waits are long or travel is hard.
Key feature 10 of 10
Tell the kidney team
Tell the kidney specialists what else in this patient's life should shape treatment choices.
CFPC skill CommunicationPhase Follow-up, referralSources Choosing Wisely Canada
On the exam
A frail 86-year-old with dementia is referred as kidney function nears dialysis. Expect one best answer.
Pick what to put in the referral.
Common mistakes
Sending labs only. The team may then plan dialysis without knowing about dementia, cancer or what the patient wants.
Approach
- Write the patient's goals and wishes in the letter, and who decides if the patient cannot.
- Name frailty, cancer, dementia and other illness that limit benefit or life.
- Dialysis should start only after a shared decision with the patient, the family and the kidney team.
- In older adults with many illnesses, limited data suggest survival may be similar with or without dialysis.
- A low eGFR alone does not start dialysis unless it falls below 6. Otherwise wait for symptoms, fluid overload, high potassium or acidosis.
Flashcards
Answer it first, then check.
KF 2Stable eGFR of 40, on metformin, contrast CT tomorrow. Stop the metformin?
No. Above 30 with no acute injury, keep it and skip the creatinine check after. Source: Canadian Association of Radiologists 2022
KF 2eGFR of 38 before a contrast CT. Give IV fluids or N-acetylcysteine?
Neither. Fluids show no benefit above 30, and N-acetylcysteine is not recommended at all. Source: Canadian Association of Radiologists 2022
KF 2Metformin was held for contrast at an eGFR of 22. When can it restart?
After at least 48 hours, if creatinine stays within 25% of baseline and the team reviews it. Source: Canadian Association of Radiologists 2022
KF 3Protein in the urine despite an ACE inhibitor. Add an ARB?
No. The pair brings low blood pressure, acute kidney injury and high potassium. Source: Choosing Wisely Canada
KF 5Kidney disease and high blood pressure, asking for ibuprofen for a sore knee. Your answer?
Avoid it. NSAIDs raise blood pressure, hold fluid and can worsen kidney function. Source: Choosing Wisely Canada
KF 6On ramipril and furosemide, vomiting, cannot keep fluids down. What is the advice?
Pause both, and get seen soon for creatinine and potassium. Restart once drinking normally.
KF 7Creatinine rising, little urine after fluids, a full bladder on scan. Next step?
Put in a catheter now. Not more fluid, not a diuretic. Image later if needed.
KF 10A frail patient with dementia nears dialysis. What must the kidney team hear?
The patient's goals, frailty, dementia and other illness. Dialysis starts only after a shared decision. Source: Choosing Wisely Canada
FAQ
Is contrast dye still a big kidney risk?
Less than once taught. Canadian radiology guidance says contrast is likely a rare cause of injury. The risk matters mainly with eGFR 30 or less, acute injury, or large doses into an artery.
Should an ACE inhibitor stop before a contrast CT?
No. The radiology guidance does not support routinely stopping ACE inhibitors, ARBs or water pills around contrast. Sick-day rules are different: they apply when the patient cannot keep fluids down.
Can I trust the eGFR in a patient who is acutely ill?
No. The eGFR assumes creatinine is steady. During acute injury it is unreliable, so follow the creatinine itself. A timed urine collection is too slow to guide a same-day decision.
Sources
Written from the CFPC Assessment Objectives and Canadian guidelines first. Checked by a Canadian family physician, MD, CCFP.
Last reviewed October 20, 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
- Canadian Association of Radiologists guidance on contrast-associated acute kidney injuryCanadian Association of Radiologists · 2022
- Choosing Wisely recommendationsChoosing Wisely Canada