Differential diagnosis (the process) can be regarded as implementing the hypothetico-deductive method in the sense that the potential presence of candidate diseases or conditions can be viewed as hypotheses which are further processed as being true or false.

Knowledge of the natural history of illnesses is requisite in determing the difference between two or among diagnostic considerations.

Performing a differential diagnostic procedure is based on the idea that one begins by considering the most common diagnosis first: a head cold versus meningitis, for example. As a reminder, medical students are taught the adage, "When you hear hoofbeats, look for horses, not zebras," which means look for the simplest, most common explanation first. Only after the simplest diagnosis has been ruled out should the clinician consider more complex or exotic diagnoses.

In some cases, there will remain no diagnosis; this suggests the physician has made an error, or that the true diagnosis is unknown to medicine. Removing diagnoses from the list is done by making observations and using tests that should have different results, depending on which diagnosis is correct.

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Differential diagnosis is a process wherein a doctor differentiates between two or more conditions that could be behind a person’s symptoms.

When making a diagnosis, a doctor may have a single theory as to the cause of a person’s symptoms. They may then order tests to confirm their suspected diagnosis.

Often, however, there is no single laboratory test that can definitively diagnose the cause of a person’s symptoms. This is because many conditions share the same or similar symptoms, and some present in a variety of different ways. To make a diagnosis, a doctor may need to use a technique called differential diagnosis.

This article describes what differential diagnosis is and provides some examples. It will also explain how to interpret the results of differential diagnosis.

What is differential diagnosis?

a doctor in a ward writing up paperwork for a differential diagnosisShare on PinterestA doctor may perform a differential diagnosis when there is no single laboratory test to diagnose the cause of a person’s symptoms.

Differential diagnosis involves making a list of possible conditions that could be causing a person’s symptoms. The doctor will base this list on information they gain from:

  • the person’s medical history, including their self-reported symptoms
  • physical examination findings
  • diagnostic testing

Less commonly in the diagnostic approach, a doctor may have one theory about the cause of a person’s symptoms and test for that one condition.

However, many conditions share some of the same or similar symptoms. This makes the underlying condition difficult to diagnose using a nondifferential diagnostic approach.

A differential diagnostic approach is helpful when there may be multiple potential causes to consider.

The goals of differential diagnosis are to:

  • narrow down the working diagnosis
  • guide medical evaluation and treatment
  • rule out life threatening or time critical conditions
  • enable the doctor to make the correct diagnosis

 

 

 

References

Fletcher RH, Fletcher SW, Wagner EH. Clinical Epidemiology, the Essentials. 3rd ed. Baltimore, MD: Williams & Wilkins; 1996