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Medical Malpractice Law and Missed Diagnoses


Medical malpractice is a complex law area involving allegations of professional negligence against healthcare providers, including physicians, nurses, and other medical professionals. In Ontario, medical malpractice cases are governed by the law of negligence, which requires the plaintiff to prove that the defendant breached a duty of care owed to the plaintiff and that this breach caused the plaintiff harm.

One common type of medical malpractice case involves missed diagnoses, where a healthcare provider fails to diagnose a medical condition or disease in a timely and accurate manner, resulting in harm to the patient. Missed diagnoses can occur in various medical settings, such as hospitals, clinics, and private practices, and can involve a wide range of medical conditions, including cancer, infections, heart disease, and other serious illnesses.


Legal Standards

In Ontario, the legal standard for assessing whether a healthcare provider has breached the duty of care in a missed diagnosis case is the “reasonable and prudent physician” standard. This standard requires healthcare providers to exercise the degree of care, skill, and knowledge that a reasonable and prudent physician in the same circumstances would have exercised. In other words, the healthcare provider’s actions or omissions will be measured against the standard of care expected of a reasonably competent healthcare professional in similar circumstances.  The healthcare provider does not have to be perfect, nor does a bad medical result necessarily mean that the healthcare provider was negligent.

To establish a claim for medical malpractice based on a missed diagnosis, the plaintiff must prove the following elements:

  1. Duty of Care: The plaintiff must establish that the healthcare provider owed a duty of care to the patient. This typically exists when there is a doctor-patient relationship, and the healthcare provider has assumed responsibility for the patient’s care.


  1. Breach of Duty: The plaintiff must prove that the healthcare provider breached the duty of care by failing to meet the standard of care expected of a reasonable and prudent physician in the same circumstances. This may involve showing that the healthcare provider failed to order appropriate diagnostic tests, failed to properly interpret test results, or failed to consider relevant medical information.


  1. Causation: The plaintiff must establish that the breach of duty caused the patient harm. This may require showing that the missed diagnosis resulted in delayed or inadequate treatment, which in turn caused the patient’s condition to worsen. This can be more difficult than one might think.  For example, if a person has late-stage cancer that has progressed passed the point of possible successful treatment, a missed diagnosed of that person’s cancer has not caused anything from a legal standpoint.


  1. Damages: The plaintiff must prove that they suffered damages as a result of the missed diagnosis, such as physical harm, emotional distress, or financial losses.


Healthcare providers facing allegations of missed diagnoses in medical malpractice cases in Ontario may raise various defenses, including:

  1. Standard of Care: The healthcare provider may argue that their actions or omissions were consistent with the standard of care expected of a reasonable and prudent physician in the same circumstances. They may present expert medical evidence to support their position.


  1. Contributory Negligence: The healthcare provider may argue that the patient contributed to their own harm by failing to follow medical advice or by providing inaccurate or incomplete medical history, which in turn affected the diagnosis and treatment.


  1. Limitation Periods: Ontario has limitation periods that restrict the time within which a plaintiff can bring a medical malpractice claim. Healthcare providers may argue that the claim is barred by the applicable limitation period.



Medical malpractice cases involving missed diagnoses are complex and require a thorough understanding of the legal and medical issues involved. Healthcare providers in Ontario should be aware of the legal standards and defenses applicable to missed diagnosis cases, and take appropriate steps to meet the standard of care expected of a reasonable and prudent physician. Patients who believe they have suffered harm due to a missed diagnosis should seek legal advice from experienced medical malpractice lawyers to understand their rights and options.




Joseph Dart is a partner at Bergeron Clifford LLP. He graduated from Yale University in New Haven, CT., in 200. He graduated from Queen’s University Law School in 2005. Joseph joined Bergeron Clifford in 2015, and represents plaintiffs in negligence, medical malpractice and auto cases.

Joseph was called to the bar in 2006, and began his legal career as a crown prosecutor in the Crown Attorney’s Office, first in Scarborough, and later in Belleville, where he worked on various high-profile criminal cases. During his time with the Crown’s Office, Joseph litigated many cases in both the provincial and superior courts of Ontario


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