What is Diagnostic Reasoning?
Diagnostic Reasoning: The Tortoise and the Hare
Most of us have heard the classic story of the tortoise and the hare (and if you haven’t – do a quick search). I like to use this analogy to illustrate a common theory behind diagnostic reasoning – system 1 and system 2 thinking. Let’s look at 2 different cases.
Case 1: You see a 3-year-old with sore throat. You’ve seen it several times before. It feels like classic pharyngitis – sore throat, tonsillar lymphadenopathy, general malaise. You complete your history, physical exam, and use the CENTOR-M score to rule in the possibly of strep pharyngitis. The rapid positive antigen test is positive, so you discuss treatment and send them on their way.
Case 2: Next you see a 30-year-old male with a 14-day history of sore throat. This doesn’t feel quite right – 14 days is a long time for a sore throat. You go through a mental checklist: could it be strep throat? Peritonsillar abscess? Epiglottitis? Mononucleosis? Is he at risk for HIV or gonococcal throat infection? Could this be a hematologic malignancy? After a history, physical exam, and reviewing a list of differential diagnoses, you perform a throat swab for gonorrhea and send him for HIV testing.
Was there a difference in your approach to these two cases? Were you conscious of it?
What is diagnostic reasoning?
The formal definition is: “the cognitive process used to collect and interpret data necessary to evaluate and manage a patient’s medical concern” (1). There are two useful schemas for diagnostic thinking: system 1 and system 2.
The Hare
System 1 thinking is sometimes referred to as your ‘gut intuition’ – it is based on pattern recognition and entails automatic information processing. Although rapid and often correct, it is more susceptible to error or biases. We often use it in patient encounters we are familiar with, like the 3-year-old with sore throat (2). Think of system 1 as the hare – it’s fast, and you get to your destination quickly.
The Tortoise
System 2 thinking refers to a slower, deliberate form of thinking based on rational judgement, application of decision rules, and is a process we can turn to during less familiar patient encounters or when something doesn’t fit the classic pattern we are used to seeing (2). Think of system 2 as the tortoise – it’s slower, thus takes time to get to your destination.
So, what is better, system 1 or system 2? In reality, both systems are useful and complement each other. The key is to have awareness (referred to as meta-cognition) into how we are thinking about a specific case. A defining feature of expert clinicians is their ability to naturally switch between schemas, relying on system 1 (intuitive) thinking for familiar and common cases, and system 2 (deliberate) thinking for less familiar or complex situations.
Key Take Home Points
Diagnostic reasoning is complex, but thankfully like any skill, can be trained with deliberate practice.
Challenge yourself: next time you’re seeing and diagnosing a patient, ask yourself – am I using system 1 or system 2 thinking?
References/Readings
Nordik CL. Integrating strategies for improving diagnostic reasoning and error reduction. Journal of the American Association of Nurse Practitioners. 2021; 33(5): 336-372. https://doi.org/10.1097/JXX.0000000000000464 (VIEW HERE)
Smith SK, Benbenek MM, Bakker, CJ, Bockwoldt D. Scoping review: Diagnostic reasoning as a component of clinical reasoning in the U.S. primary care nurse practitioner education. Journal of Advanced Nursing. 2022;78(12): 3869-3896. https://doi.org/10.1111/jan.15414 (VIEW HERE)
Another resource: 2. Monteiro SM, Norman G. Diagnostic Reasoning: Where We've Been, Where We're Going. Teaching and learning in medicine. 2013;25(sup1):S26-S32. (VIEW HERE)