The differential diagnosis is the systematic list of possible conditions that a clinician considers when assessing a patient’s presentation. In medical malpractice litigation, the adequacy of the differential diagnosis is often the central question in standard-of-care analysis, particularly in failure-to-diagnose, misdiagnosis, and delayed-diagnosis claims. A common allegation is that a reasonable practitioner in the same circumstances would have included a particular condition on the differential, would have ordered investigations directed at ruling that condition in or out, and would have arrived at the correct diagnosis as a result.
Differential diagnosis analysis is contextual. The same presentation that warrants a wide differential in an emergency department may warrant a narrower one in a primary care follow-up visit, because the pre-test probability of high-acuity conditions is different. Time pressure, patient volume, available investigations, and the clinical history all shape what reasonable practitioners actually do, and expert evidence is needed at every step to translate clinical practice into the legal standard of care.
Anchoring bias, where a clinician fixes on the first plausible diagnosis and stops considering alternatives, is a recurring theme in both the medical literature on diagnostic error and in the judicial reasons addressing it.
Posts tagged Differential Diagnosis analyze Ontario decisions in which the adequacy of the practitioner’s diagnostic reasoning was at issue.
BC court dismisses ED malpractice claim involving missed subarachnoid hemorrhage where patient lacked thunderclap headache and the bleed had not yet occurred.
Ontario ER physician suspended after sending home a 19-year-old with a peritonitic abdomen; she died of septic shock. CPSO v Duic, 2025 ONPSDT 11.
The BC Supreme Court dismisses a missed-appendicitis claim. Normal ultrasound, documented differential diagnosis, and the anchoring bias allegation rejected.
The Saskatchewan Court of Appeal affirms dismissal of a failure-to-refer claim. Breach of standard of care, but causation defeated by referral wait times.
A delayed-diagnosis cancer claim was dismissed at standard of care and causation, with a 40% contributory negligence finding for repeated failures to follow up.
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