Cognitive bias leading to missed diagnosis and patient death

Key messages from the case

Diagnostic error is often the result of multiple contributing factors rather than a single mistake. Cognitive errors can occur in any clinical setting and with any patient. These errors may arise from failures in gathering, interpreting, or acting on clinical information, as well as from cognitive biases such as anchoring and premature diagnostic closure.

The risk of diagnostic error is increased in complex care environments involving multiple clinicians with differing levels of experience, particularly where supervision, communication, and clinical handover are inadequate.

Details of the decision

Mr H, an Aboriginal man, presented to a regional hospital emergency department with severe abdominal pain, describing a ‘popping’ sensation in his abdomen. Upon initial triage, he told staff that he had smoked marijuana earlier that day and had a history of alcohol use.

Mr H was admitted to the emergency department and assessed by a junior medical officer, Dr T, who diagnosed undifferentiated abdominal pain. Dr T documented that Mr H reported no nausea or vomiting. She also documented that Mr H had smoked a small amount of marijuana that day and had taken amphetamines two days earlier.

Dr T discussed her findings with her supervisor, Dr N, who provided a provisional diagnosis of cannabinoid hyperemesis syndrome (CHS). Dr T was unfamiliar with this condition and relied on her supervisor’s provisional diagnosis. Dr N recommended that Mr H be treated with intravenous fluids and analgesia, monitored for 24 hours, and then discharged.

Dr T documented this plan and prepared a discharge summary, despite discharge not being planned until the following day. Apart from preliminary blood tests, no further investigations, including imaging, were ordered.

Mr H was monitored over the next 18 hours in the Short Stay Unit (SSU). Care was handed over from Dr N to Dr B with the provisional diagnosis of CHS. The handover did not include a documented review of the clinical records.

The following morning, care of Mr H was handed over from Dr B to Dr E. This handover was not documented. Dr E later stated that he was not informed that Mr H had been persistently tachycardic during his admission or that he had required analgesia overnight. Dr E did not review Mr H prior to discharge.

Mr H was discharged with ibuprofen and paracetamol and advised to return if his pain worsened. Although he was still experiencing pain, he told nursing staff that he wished to go home.

He later stayed at a relative’s home and was found deceased the following day. Post-mortem examination determined the cause of death to be perforated duodenal ulcers. Toxicology and microbiology testing identified the presence of staphylococcus, streptococcus, and E. coli.

Diagnostic error – cognitive bias

The coroner identified multiple cognitive biases contributing to the missed diagnosis.

Dr N acknowledged that his initial impression of the patient led to anchoring bias and premature diagnostic closure. The provisional diagnosis of CHS was formed early and was not subsequently reassessed through direct patient review or further investigation, such as imaging. As a result, clinical features inconsistent with CHS were not adequately considered.

Despite the absence of nausea or vomiting and the presence of persistent tachycardia and ongoing pain, the working diagnosis was not questioned. The coroner found that the diagnosis of CHS was maintained despite limited supporting clinical evidence.

A further contributing factor was a lack of knowledge and the presence of an authority gradient. Dr T did not feel able to question the provisional diagnosis provided by her senior colleague. This reduced the likelihood that alternative diagnoses would be raised or investigated.

Other clinicians involved in Mr H’s care accepted the provisional diagnosis without independently reassessing the patient or the diagnostic reasoning. This represented a further form of anchoring bias, compounded by inadequate handover and failure to respond to ongoing abnormal observations.

The coroner concluded that the missed diagnosis resulted from cognitive bias, inadequate reassessment and failures in supervision and handover.

Cultural safety

During the inquest there was evidence about racial bias, culturally safe provision of healthcare and the role Mr H’s Aboriginality played in his care. The coroner found that when Dr N diagnosed CHS, he did not know the patient identified as Aboriginal, so there was no basis for finding that the doctor diagnosed the patient with CHS because he was Aboriginal.  The evidence was that no real attention was given to Mr H’s Aboriginality.

The coroner noted that Mr H’s story provided a significant opportunity to reflect on the importance of Aboriginality in informing medical treatment.  The coroner therefore made recommendations aimed at improving cultural safety and health outcomes for First Nations people. 

Outcome

The coroner made several recommendations, including:

• Changes to protocols for documenting management plans.
• Requiring senior medical officer approval for discharge from the Short Stay Unit.
• Referral of Dr N’s treatment of Mr H to the medical regulator.

Key lessons

To reduce the risk of cognitive bias leading to diagnostic error:

• Be alert to anchoring bias and premature diagnostic closure, particularly when a diagnosis is made early in a patient’s presentation.
• Use a ‘diagnostic time-out’ to consciously reassess whether the working diagnosis fits the evolving clinical picture.
• Actively consider and document differential diagnoses, especially when symptoms persist or worsen.
• Ensure effective clinical handover, including communication of unresolved concerns and abnormal observations.
• Encourage junior clinicians to question diagnoses and escalate concerns, and foster a culture where diagnostic uncertainty can be openly discussed.

References and further reading

Avant factsheet: Reducing diagnostic error

Avant factsheet: Missed or delayed diagnosis

Avant eLearning: Reducing diagnostic error

For medico-legal advice, please contact us here, or call 1800 128 268, 24/7 in emergencies.