A Randomized Cohort Study of Diagnostic and Therapeutic Thresholds in Medical Student Clinical Reasoning.

PURPOSE: Learning to make decisions under uncertain conditions is a critical component of diagnostic and therapeutic reasoning. This study sought to determine treatment decisions medical students make when presented with different thresholds of diagnostic uncertainty and whether they appropriately adjust diagnostic probabilities with test information.

METHOD: Two classes (2015, 2016) of fourth-year students (N = 342) were presented a patient with viral pneumonia and given 10%, 20%, or 50% pretest probabilities of that patient having a superimposed bacterial infection. Students decided to not treat, order a diagnostic test to guide management, or treat without testing based on these probabilities. The 2015 class was provided a posttest probability of 10% or 50% and asked to adjust their initial treatment decision.

RESULTS: When given a low (10%) pretest probability, students were less likely to decide to treat (6%) and more likely to decide not to treat (36%). The percentage of students deciding to treat increased as the pretest probability of a superimposed infection increased from 10% to 50%, while the percentage of students not wanting to treat decreased. Interestingly, at 10%, 20%, and 50% pretest probability levels, most students were unable to decide and chose to order another test (57%, 67%, and 64%, respectively). When provided low and high posttest probabilities, students appropriately adjusted their decision making, but 29% to 32% still wanted additional testing.

CONCLUSIONS: Students adjusted treatment decisions to reflect different levels of diagnostic uncertainty, but varied considerably in their individual thresholds to make decisions, possibly contributing to unnecessary testing.