Diagnosis: unconscious or conscious bias?

5 minute read

As doctors we bring our biases, and occasionally our prejudices, into the diagnostic arena, says Professor Leon Piterman


Our time-honoured clinical method consists of history taking, physical examination and investigation.

The purpose of undertaking this exercise is to achieve a correct diagnosis to which we attach a prognosis and advise treatment or management.

We are taught that “careful” history taking is key to diagnosis and that 70% of diagnoses can be based on history alone. We also know that “careful” has a different meaning to experienced practitioners, specialists, junior doctors and medical students.

Experienced practitioners, both GPs and specialists, focus their questioning on highly critical cues. Medical students and junior doctors take a systematic approach to history taking and may not differentiate the weight of each presenting symptom. Reliance on investigations (often unnecessary) seems to dominate the diagnostic process in these circumstances.

When I was a neurology registrar in outpatients my boss was in the habit of seeing all new patients first and taking a history, but not undertaking a physical examination or arranging tests before he had passed them over to me.

He then wrote down the diagnosis and asked me to check once I had completed a second round of history-taking as well as physical examination and investigations. He was never wrong.

Past experience, an appreciation of personal heuristics – he had heard and seen it all before   – enhanced the positive predictive value of his history taking. In general practice, while we may appear to take shortcuts, we adopt similar practices. We are also informed and influenced by our past knowledge of the patient and the prevailing local epidemiology of diseases, particularly seasonal variations.

So is the diagnostic process scientific? Is it free of bias?

The following cases tend to suggest that it is anything but scientific. We do not operate in a bias-free zone. We bring our biases, and occasionally our prejudices, into the diagnostic arena.


Bill, aged 68, had been attending our clinic for more than 20 years. His plethoric facial appearance, complemented by a number of scars, his knobbly hands and truncal obesity bore witness to his battles with alcohol, not to mention battles with the demons that his service in Vietnam had inflicted on him.

Over the past decade he had developed hypertension, type 2 diabetes and fatty liver and suffered several attacks of gout. His marriage had failed long ago, his children were estranged, and the pub and the pokies provided the only relief from the boredom of the daily routine.

On this occasion Bill was squeezed in as an extra on a busy Monday morning. He limped into my consulting room, unshaven and distressed. He wore a loose fitting slipper on one foot and a worn-out shoe on the other.

I didn’t feel the need to take history. The diagnosis seemed quite obvious.

“Hi Bill, take a seat. So you have another attack of gout,” I remarked.

“No doc,” he replied, “I dropped a full gas bottle on my foot when I was trying to fix the BBQ.”


Ethel was a 58-year-old brittle diabetic. I had a call from her visiting daughter, Jane,  requesting an urgent home visit as her mother was having a “hypo” and she could not get any sweets or juice into her.

I rushed to Ethel’s home to find her slumped in a chair in the kitchen, sweaty and semiconscious. I administered some IV glucose and IM glucagon and arranged an ambulance to take Ethel to the local ED.

What struck me as I walked into the small, single-fronted timber home was the chaotic nature of the living room and the kitchen. There were boxes of leaves and tree branches strewn everywhere. It was as if Ethel had been collecting garden refuse and storing it in her home.

Restoring her blood sugar to normal seemed easy compared with unravelling the mess in her home. I felt compelled to express my concern to her daughter about Ethel’s general wellbeing, physical and mental, and her ability to cope on her own.

Jane politely informed me that Ethel was an artist and used leaves, branches and other plants as part of her artwork. She then handed me an invitation to an exhibition that Ethel was having at a local gallery in three weeks’ time and asked if I thought Ethel would be fit enough to make it.

In both cases I very quickly learned that things are not always what they seem.

Medicine is an observational science but observations in both instances were coloured by bias.

In Bill’s case his past history drew me to a rapid fire diagnosis in the absence of taking a skerrick of history.

It is not uncommon to postulate diagnostic hypotheses as soon as the patient walks in the room. After all we use all of our powers of observation.  But hypotheses should remain as such until further evidence raises their level of probability.

In Ethel’s case I jumped too quickly to a social diagnosis informed by a biased view of her environment.

Observation is important but looking should be accompanied by careful listening and cautious responding.

I learned my lesson.

Leon Piterman is Professor of General Practice at Monash University and has been in clinical practice for almost 40 years.

Do you have similar professional experiences you would like to share? Please email: grant@medicalrepublic.com.au

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