Moving Us Closer To Osler
A Miller Coulson Academy of Clinical Excellence Initiative

A Series of Biases: Murphy’s Law at Play


Biases get in the way of our clinical reasoning. When the data doesn't fit, clinically excellent providers re-examine their assumptions.

As a new physician, I am always worried about missing something obvious in my patient’s history, physical exam, or investigations. I have trained my mind to look at things multiple times before making a decision.


As an educator, one of the first things I tell medical students, residents, and PA fellows is that no question is silly; the fact that you have a question means that you are thinking and these questions help your colleagues to step back and reflect.


I recently had the privilege of taking care of a very pleasant 83-year-old man. He had a known history of prediabetes, CAD, HTN, HLD, and lung cancer in remission who presented to the ED with complaints of left leg pain and swelling. His vitals and labs were normal. The contrast CT of his left lower extremity revealed soft tissue swelling. In light of erythema noted on exam, he was treated for cellulitis with parenteral antibiotics. The admitting physician concurred with the diagnosis and continued antibiotics.


The following morning, I was the rounding physician for the patient. Upon chart review, it appeared to be a straightforward case of cellulitis that required IV antibiotics for a couple of days with transition to oral antibiotics and discharge. Simple!


However, that was not the case. On bedside exam and repeat history for the patient, I noticed that he had bilateral leg swelling—and in fact, his right leg was noticeably more swollen. I also did not see any erythema on his left leg. Furthermore, there was no area demarcated by the usual tracing. The patient had received one dose of parenteral antibiotics. Asymmetric bilateral leg edema was missed on previous assessments. Moderate Wells score and the absence of infectious markers prompted me to seek an alternate diagnosis. I ordered the lower extremity venous ultrasound, which revealed bilateral peroneal and right posterior tibial vein DVT for which anticoagulation was started.


Below are the biases that delayed reaching the correct diagnosis.



1.Chief complaint of unilateral leg pain and failure to probe into contralateral leg symptoms led to a framing bias by several providers.


2.CT findings contributed to premature closure thereby substantiating the incorrect diagnosis of cellulitis.


3.Admitting team carried forward the diagnostic momentum, administering incorrect treatment, which was a case of anchoring bias.


Bayesian thinking:

1.The subsequent team of providers reframed the problem using the new clinical information of asymmetric bilateral swelling (as opposed to unilateral) in a cancer patient, and a validated decision making tool (Wells score). When doing so, ordering appropriate testing (the ultrasonography) was clearly necessary.


2.Irrespective of unilateral edema versus bilateral asymmetric edema, asymmetric calf swelling, and ≥2 cm difference has a positive likelihood ratio of 2.1 (increased probability of DVT by 15%).


I found the following questions that Drs. Feinbloom and Krakow mentioned in their article “Diagnose Misdiagnosis,” in “The Hospitalist” very helpful for patient care:


1.What do I think it is and what can’t I miss today?


2.Which data fit and which don’t?


3.How does the test not show what I expected? Is that because it’s wrong or I’m wrong?


4.What are the worst things this could be?


5.What are the most likely things this could be?


6.What are the highly unusual things this can be?


I noticed the oversight this time, but there are likely other mistakes that I am unaware of.


It is imperative to have a non-punitive, non-judgmental reporting system for such diagnostics errors for physicians, so we can continue to grow and to improve our clinical reasoning and patient care.