A differential diagnosis is a list of possible conditions that share the same symptoms. For example, fatigue can be a symptom of anemia, depression, heart disease, thyroid disease, and many other conditions.
A 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.
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
Differential diagnosis can take time. For a doctor to determine the correct diagnosis, they will follow the steps below.
1. Take a medical history
When preparing for differential diagnosis, a doctor will need to take a person’s full medical history. Some questions they may ask include:
- What are your symptoms?
- How long have you been experiencing symptoms?
- Do you have a family history of certain conditions?
- Have you traveled out of the country recently?
It is important that a person answers all questions honestly and in as much detail as possible.
2. Perform a physical exam
Next, a doctor will want to perform a basic medical examination. The examination may include the following:
- taking the person’s heart rate
- taking their blood pressure
- listening to their lungs or examining other areas of the body from which symptoms may be originating
3. Conduct diagnostic tests
After taking a medical history and performing a physical examination, the doctor may have some ideas as to what may be causing a person’s symptoms.
They may order one or more diagnostic tests to rule out certain conditions. Such tests may include:
- blood tests
- urine tests
- diagnostic imaging tests, such as:
4. Send the person for referrals or consultations
In some cases, the doctor may feel that they do not have the specific expertise to diagnose the exact cause of a person’s symptoms. In such cases, they may refer the person to a specialist for a second opinion.
It is not uncommon for multiple doctors to review one patient during differential diagnosis.
Below are three examples of common differential diagnoses.
Chest pain is a symptom that can have many causes. Some are relatively mild, whereas others are serious and require immediate medical attention.
If a person is experiencing chest pain, a doctor will need to ask questions to determine certain factors, such as the location, severity, and frequency of the pain.
These questions may include the following:
- How do you feel? Describe the sensation.
- Where does it hurt?
- Does the pain extend to any other part of your body?
- Did anything trigger the pain?
- How long has the pain lasted?
- Has anything made the pain better or worse?
- Have you experienced any other symptoms?
By asking these questions, the doctor will hopefully be able to categorize the chest pain as one of the following types:
- Cardiac: These conditions relate to the heart. Examples include unstable angina and heart attack.
- Pulmonary: These conditions relate to the lungs. Examples include:
- Gastrointestinal: These conditions relate to the digestive system. Examples include gastroesophageal reflux disease, which can lead to Barrett’s esophagus, and peptic ulcers.
- Musculoskeletal: These conditions relate to the muscles, bones, and connective tissues. Examples include fractured ribs and other trauma to the chest wall or sternum.
- Miscellaneous: This category describes other potential causes of chest pain, such as:
Once the doctor has narrowed down the type of pain, they will order diagnostic tests to determine the potential cause of the pain. These tests may include:
Headaches are a common issue. Because of this, it can be difficult for a doctor to determine when a headache is a benign irritation, and when it is a serious health concern.
During differential diagnosis, a doctor will look for certain red flags that indicate that the headache is more than just an inconvenience. These red flags include the sudden onset of severe headache and headache following head trauma.
The sudden onset of severe headache could indicate several underlying conditions, such as subarachnoid hemorrhage or pituitary apoplexy. Headache following head trauma could indicate intracranial hemorrhage, subdural hematoma, or epidural hematoma.
The doctor will ask the following questions to determine whether or not the headache poses a serious risk to the person’s health:
- Did the headache start gradually or suddenly?
- Did anything trigger the headache?
- Where is the pain?
- Does the pain seem to spread to any other area? If so, where?
- What kind of pain do you have? Is it throbbing, stabbing, dull, or something else?
- How bad is your pain, on a scale of 1 to 10?
- Do you have headaches regularly?
- Is this your first or worst headache?
- Is this headache like the ones you usually have?
- Do you have other symptoms that occur with the headache?
In some cases, the doctor may perform a neurological exam. This exam may assess multiple factors, including:
- the pupils’ responses to light
- responses to or sensation of touch
- deep tendon reflexes
- motor strength
A medical history and physical exam can narrow down the possible causes of headache. Neuroimaging tests using CT or MRI scans can help rule out or confirm certain diagnoses.
Stroke requires prompt diagnosis and treatment. Because of this, many doctors turn to a differential diagnostic method when considering the possibility of a stroke.
During the physical examination, a doctor will check a person for the following symptoms of a stroke:
- reduced mental alertness
- problems with coordination and balance
- problems with vision
- numbness or weakness of the face, arms, or legs
- difficulty speaking or communicating
The doctor will look through a person’s medical history to see if they have any medical conditions that may increase their risk of stroke. Such conditions include:
The doctor will then order one or more of the following tests:
- blood tests
- a CT scan, to look for possible bleeding on the brain
- an MRI scan, to check the brain tissue for signs of damage
- an ECG or EKG, to look for heart problems that could have caused a stroke
A person may require multiple in-office examinations and diagnostic tests before they receive a definitive diagnosis.
Some patients may have multiple negative test results before they get a diagnosis. However, each negative test result brings the doctor one step closer to figuring out the cause of a person’s symptoms.
Some people may need to begin treatment before a doctor has confirmed their diagnosis. This may be the case if one of the potential causes of a person’s symptoms requires prompt treatment to prevent further complications.
A person’s response to a particular treatment can itself provide valuable insights into the cause of their symptoms.
Differential diagnosis refers to a list of possible conditions that may be causing a person’s symptoms. A doctor will base this list on several factors, including a person’s medical history and the results of any physical examinations and diagnostic tests.
Many conditions share the same symptoms. This can make certain conditions difficult to diagnose using a nondifferential diagnostic approach. A differential diagnostic approach may be necessary in cases where there is more than one potential cause of a person’s symptoms.
Undergoing differential diagnosis can be a long, worrying, and frustrating process. However, it is a rational and systematic approach that can allow a doctor to correctly pinpoint the underlying cause of a person’s symptoms.