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.

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

1. Diagnostic reasoning is complex, but thankfully like any skill, can be trained with deliberate practice.

2. Challenge yourself: next time you’re seeing and diagnosing a patient, ask yourself – am I using system 1 or system 2 thinking?  

 References/Readings

1. 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)

2. 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)

3. 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)