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Diagnosis is the art of identifying a disease by the signs, symptoms, and test results of a patient. Diagnosis stems from the Greek word, diagignoskein, which means to distinguish or discern. Indeed, the ability to distinguish or discern a patient’s underlying illness is critical to being an effective clinician as a hospital medicine provider. In many cases, hospitalized patients may be quite complicated with multiple competing possible reasons to explain their underlying signs or symptoms. Patients do not always read textbook (ie, they may not always describe their symptoms or have findings on exam that are pathognomonic or as classically described). Therefore, diagnostic reasoning and diagnostic decision making are crucial skills for hospital medicine providers. In addition, cognitive biases exist and diagnostic errors occur when there is any mistake or failure in the diagnostic process that leads to a misdiagnosis, a missed diagnosis, or a delayed diagnosis. This chapter will discuss diagnostic reasoning and diagnostic decision making.



Clinical reasoning is the process where a clinician applies reasoning in combination with the clinician’s knowledge and skills (Figure 8-1). Clinical reasoning is a constant process that does not end when the diagnosis has been made. It may be considered complete upon autopsy or when a gold standard has confirmed a diagnosis, but it is important to acknowledge that in many instances the gold standard is not 100% accurate. In the hospital setting clinicians are operating under a running diagnosis until the diagnosis has been confirmed and/or until the patient has improved both subjectively and objectively. Sometimes patients do not improve when a treatment strategy is implemented; thus, it is important that providers continuously use clinical reasoning skills as information is collected in an attempt to verify the diagnosis. Once a treatment or workup plan has been implemented, it is crucial to reassess the patient’s response to this to further confirm if the correct diagnosis or treatment strategy has been made (Figure 8-2). If the diagnosis does not appear correct or the treatment strategy is failing, the clinician must review the information and data collected and reconsider the other possible diagnoses to explain a patient’s presenting signs and symptoms. Hence, a clinician’s ability to successfully reason and diagnose is in some ways anchored by that clinician’s ability to create an adequate differential diagnosis.

Figure 8-2

The process of clinical reasoning.


A differential diagnosis is more than just a list of illnesses that potentially explain why a particular sign, symptom, and/or diagnostic test result exists. Rather, the clinician uses the differential diagnosis to distinguish a disease or condition from others that ...

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